First of all, the artwork isn't very good. Now I don't expect you to be a super-amazing perfect artist, and I'm not holding you to some impossible standard. If fan-cases can look super polished and everything that's really nice, but not a requirement. However, what you have so far looks like you traced over the official artwork with minor variations and then used the fill bucket to color it. The result makes it look flat, messy, and overall uninspired. It doesn't look like much time was put into it, and the fill bucket areas are very noticeable, because they're aliased, and thus aren't smoothly integrated with the lines. The line-work is also pretty sloppy, being basically just an outline, and the images lack depth; it looks like a cardboard cutout rather than a character. The work is noticeably bad, and this is a problem because while the art doesn't need to be professional-level, it draws attention because it isn't particularly well-done. It looks effortless and flat, and actually detracts from the case instead of adding to it. To fix this, you really just need practice. Practice drawing and take classes to improve, or work on regular paper and scan it. I highly suggest Life Drawing classes, as they really help you get a handle on the figure, like so:
What you want to get down is structure. Drawing bodies is essentially building a person one piece at a time, and trying to get each one right. Things have to be in proportion, they have to have depth, and they have to make sense. Now, obviously, these things don't necessarily apply when you're doing, say, cartoons, but the basic principles always apply. You have to learn the basics first and then move on to other stuff. But like I said, this can all be learned. You just need practice.
For now, if you still want to make this happen, I suggest looking for an artist to do your work.
However, that brings me to my second point: the designs. Again, this suffers from being traced art, so these characters' designs are basically limited by the official art. Lance Edgeworth is simply Edgeworth with glasses minus the cravat, and Clay Justice is Phoenix with different hair, glasses, etc. Whenever someone looks at these, they won't see "Clay Justice"-- They'll see an edit of Phoenix Wright. The only one that looks original is Maria Justice, and even then, she doesn't look too striking. I'll get to her more later. Basically, these designs don't invoke much new about these characters. They're hardly designs, because they only change details from the original art. Imagine if Clay Justice put on a blue suit, or Lance Edgeworth put on a cravat. This needs more thought and effort. Also of note, the names don't seem very inventive either. "Clay Justice" and "Greg Edgeworth" are a nice nods to canon, but other than that, the rest of the names don't seem inspired nor really connected to anything, and they aren't really punny either.
Now, I think I understand what you meant with this; it's "Generations" so clearly they'd have to sort of look like their predecessors. Unfortunately, that doesn't come across in the design. They just look like slightly altered versions of the characters we already know. This isn't good, because it's not so much a "new generation" as it is a "slightly different one", and sort of defeats the purpose of the series.
Since you haven't put up anything about story, I'll go right ahead to my last issue; the characters themselves. Now, I'm sure you have plans for them and ideas and such that you haven't put up here. But what I'm seeing here doesn't seem like well-constructed personalities. They seem more like lists of things about them, and I don't get much vibe of, say, how they'd act in court, during an investigation, when on the stand, etc. And a lot of things about them seem... odd.
Clay Justice: Okay, son of Apollo and Athena. That's fine, but does he reflect that? He's a "Whizkid" who seems entirely destined to be an ace lawyer from birth. I'd like to make it clear that I'm not calling Sue on this guy or any of them, but it seems a bit underwhelming and predictable to go with the "in the blood" thing for this. What could make it interesting is if he's, say, actually not a very GOOD lawyer, and risks disappointing BOTH his Ace Attorney parents. Again, the only actual tidbit we get about his personality is that he's "calm and collected", and doesn't get angry "except for certain times". What are those times? What makes him mad? Everyone gets angry in "certain times"; it's what those times are that set us apart. I can connect this statement of "Calm and collected but gets mad at times" to multiple characters, and it doesn't give me a good idea of who he is. This wouldn't be so bad, but the rest of his profile is just facts about him. His hobby is building, he's really smart, he memorized a novel on Edgeworth. Those are things he does/is, but it doesn't tell me much about him. I mean I could guess, but that's not really the same. And his "interesting facts".... aren't. His first word is "Objection" (again, this is kinda borderline "chosen one" stuff and really predictable), he built two treadmills for his sister (this could be better worded as, "he has a close bond with his sister and regularly builds her stuff", or did he just build them because he was bored? I don't really know.) and "his voice is lower than his father's". Good? This is problematic because I'm looking at our main protagonist and I'm not getting much except that he's a really good lawyer and he likes to build stuff. There's little personality-- And that's especially bad when you're doing an AA case, where AA is ALL about personality-filled lawyers. You've got stuff down, but it's the wrong stuff in the wrong places. Tell me about things I'd be interested in, like, say, his relationship with his parents. It didn't once feel like this guy was the kin of either Apollo or Athena. He lacks Athena's energy and Apollo's passion. He doesn't have to solely take traits from them, but there should be a resemblance. I feel like I could change this guy's name and nothing would be lost.
Maria Justice: According to the OP, she's the "trusty female sidekick we all love and know throughout the GyakuSai franchise." Just a bit of warning... this makes your character seem really stock right off the bat. I'm now not thinking of her as "Apollo and Athena's daughter", but rather "the protagonist's sidekick". Okay, so like her brother she's going into law. A bit predictable, but she's not specifically being a lawyer so I can buy it a bit more. Ultimately, she suffers from the same issues as above. I can see the exercise/energy thing from Athena, but that's about it. I could change her name and nothing would be lost. The facts all seem to be highly irrelevant, like the fact that she "likes to wear skimpy clothing". This alone isn't a bad thing, girls can wear whatever they like. But it's brought up again with "she's liked to wear skimpy clothing since she was 12". First off, a bit creepy. Second, why is that relevant? I doubt that will come up in a trial, and it's a bit odd, like I said before. Maybe you can think "why does she like wearing skimpy clothes"? I mean, this doesn't require justification, but otherwise, we can tell that from her artwork. Her interesting facts are also highly irrelevant. "She enjoys exercising more than anything else" was already stated before, and "despite the fact that her brother prefers the PlayStation brand, she has a like for the Xbox" is both out-of-nowhere and weird. (Mostly because brand-name stuff isn't usually included in the PW universe.) What I took away from this bio was "Likes exercise", "is the assistant" and "likes to wear skimpy clothing". Those things do not a personality make.
Next we have Percy Wright, who doesn't have much there, so I can't really say anything on him. The only thing I find head-tilting about him is that he's Clay's "protege". Really? Clay is about 22 and most lawyers that age wouldn't have a protege. Phoenix was just starting out at that age, and it's a bit weird that the protagonist is also a mentor-- Usually it's the other way around, with the protagonist growing to surpass their mentor.
Ryan Blackquill: oooookay. Now I notice that you like to put Japanese version of the characters' names and stuff. That's cool and all, but again, relevancy. Unless you're doing a Japanese version of the game, it doesn't really matter what he'd be called in Japan. And this is where it gets to be a problem because now we have some confusion. First off "illegitimate son"... I don't even want to go into the implications of this. It's another thing that's just off-putting here and shakes up the tone. Second: "He was born to a Japanese mother, so he was given a Japanese given name." This... okay this is confusing. Now, I presume this is referring to the Japanese version of his name? Except... In the Japanese version, that's kind of a given. Simon is Japanese in the Japanese version. But it creates a problem because "Ryan" is not a Japanese name, so now, this fact becomes confusing. I suggest rewording this fact, or outright removing it, since it's really irrelevant either way. I wasn't exactly wondering "why does he have a Japanese given name". Third: "He is like his father in many ways, except for the manipulative part, that is." Okay, this part is dangerous. Because with a description like that, many people will take this as "he's a Blackquill expy. Great." and the artwork doesn't exactly dissuade this notion. What would be better here is HOW he's like his father; he likes Japanese culture, he acts like a samurai, etc etc. And he's not manipulative, so he just... Acts like a samurai in court? Quirky, but again, we already had that. This part is dangerous because following it makes it stop being "a new generation" and just "a generation xerox". Lastly: "He bought his sword from an antique shop in Japan." This is irrelevant.
The Edgeworth Brothers: I'm covering them together cause there's not a ton to go on. Alright, so: again, no real connection to the canon characters beyond the name. They are exactly what you'd expect Edgeworth's sons to be; law enforcement, prosecutor... very predictable. There's not enough else to go off of here, but keep in mind what I said before. Also, another thing: a lot of characters seem to be Clay's childhood friend. I don't doubt this; it makes sense considering the company, but what does it mean? What's their friendship like? How do they get along? It seems just really weird and unnatural for all these connected people to all just come together and do the exact same thing their parents did. It's like nothing at all has changed except the names and faces. Another thing too; your characters seem to all have a lot of names. And again, I question relevancy on middle-names. There's a lot of irrelevant and random data here, and it doesn't add up to make an interesting or intriguing character; just general facts about this character that doesn't tell me much or get me interested. Their relationships, their likes, dislikes, what they want, why they want it, how they plan to get it; I can't imagine these people, say, hanging out, relaxing together, working together, or even talking with their parents. And on that topic, will the parents be appearing at all? What's their role in all this? It seems like they just had kids and then went "okay bye kids have fun".
In essence... I think the concept at its core is pretty flawed. So far it just looks like it's doing the same thing as before, without anything fresh or new to discover. The characters won't have any new or interesting back stories, because we already know about their families and stuff. I don't believe we'll really want to get in-depth with "how X and Y got together and made Z". It's hard to think of any story that can BE interesting with this cast. The protagonist isn't exactly going anywhere-- He's already a whiz kid and a genius, so it's not like Phoenix or Apollo's struggle. The prosecutor is already his childhood friend, so it's not like he's got to develop a relationship there like Phoenix did with Edgeworth (though they too were childhood friends, but that's more of a sidenote. I don't see any of the underlying drama with these characters; they all sound pretty buddy-buddy) so there's no drama to speak of. At most, this can be a series about a bunch of characters solving crimes and working together and stuff, but at worst it'll be boring and uninteresting. I urge you to think about the direction and purpose of this case and I suggest using
Apollo Justice as something of a reference. GS4 was intended to be, in essence, this. A new generation of Ace Attorney. Old faces return, but the spotlight is squared solely on a newcomer that's ready to start his own saga. I won't tell you that's how to write your case, but I highly urge you to think about it more.
I hope I haven't discouraged you too much with this. I get that you're enthusiastic, and I really don't want to hurt that. Enthusiasm is a great thing and from what I can tell you've got plenty of it. But it needs to be channeled in the right direction, and if you don't completely shelve this to work on your other project, then at least spend your free time making it interesting. Your other project seems promising and you're clearly putting work into that one, but I think your enthusiasm tends to get the better of you. I hope I haven't come across too harsh and I really hope this has helped you out. Sorry this was such a long read, but I felt like I had to say something, because I haven't seen anyone else really say it. So with that, I wish you the best of luck with your work.