Your idea for Lucia is interesting.
Beryl already has a gimmick to make her stand out she has a scar that reacts to demonic energy.(that and the fact that she uses an anti-tank rifle in a series where the main charicters tend to prefer pistols)
Kat fills Kat's role there is no reason to put another charicter in that role and Patty doesn't fit that type of role anyway
To "flesh out" a charicter means building up from their established personality not compleatly replacing it. Kyrie is kind, caring, and supportive but not a fighter. Devil May Cry has more than enough female charicters in battle it can survive having a few that help in a different way.
Well I think the problem with Trish is that this new Dante might not have a relationship with his mom or know who she is so it might not be wise to play up that angle. It might be easier just to bring Eva back and save trish for a sequel.
If you still want to use her, I got two ideas.
1. We are going full-cock and making her a genuine clone or shade of eva complete with the little tics that make Eva, Eva. Think more like Sloth the Homonculi from the first Fullmetal Alchemist anime and Dom's wife from Inception. It would be more psychological horror-ish if Dante was confused and actually thought he was fighting his mom, in mind, body and soul rather than just body.
2. Rather than Trish looking like the mom he doesnt really know about, I was thinking of making her look like someone he knows in the present, like a comrade within the organization. Jessica who is Grue the bounty hunter's daughter from the first novel might be up for it. Having an angel taking over his friends body and not knowing the consequences of her action might be interesting. Plus having all of her friends and relatives reacting to Trish's intrusion in their lives and trying to figure out how to deal might be fun to chart.
We gotta make that into something more useful and defined. How does her scar work anyway?
To be honest, Patty is only 8 so its hard to know what she would be like when she is older. Plus she does have witch powers and she is hanging around devil hunters so maybe they could teach her some things.
So if i was writing this thing, I would probably just use patty or fold her into Kat. Since we already have Kat, Patty would just be a minor background character. Kyrie would have more importance.
Well people hated Kyrie since she was weak and only existed to be the damsel.So if we are gonna bring her back, we might as well make more capable. The next for her character in the old series was to learn how too fight anyway, reasoning that if she was gonna be with a guy who hunts demons, she would have to learn how to defend herself if god forbid she was cornered on her own.
She doesnt have to a badass, just able to protect herself and able to contribute in a "all hands on deck"scenario outside of medic and book support.