Radomus: Mew, because he is so versatile and has a different outfit for everything (like how Mew can learn all the TMs)
Shade: Giritina? I'm not sure, he does kinda vanish a ton and Giritinia is pretty much the only ghost legend.
Oh sweet mercy I should have seen this one a while ago because it's one of my favorites, but Victoria and Victini perhaps?
Julia: There are a ton of electric legends (relatively speaking). Probably Raikou out of them though since he runs around a lot, as if he had just ingested all the coffee in the Peridot Ward.
Florina: Aren't many grass type legends left, but I wouldn't say that the remaining ones suit her well. Celibi? Too energetic and full of emotions. Shamin? Again, too energetic and playful. I'm thinking a Regi would work well with Flobot.
Corey: I can't think of many that would work well with him off the top of my head. Mewtwo is pretty hard and cynical of life and pretty much like "life is misery, life is pain."
Kiki: Cobalion, the teacher and leader who would protect the innocents
Aya: Shy and withdrawn, and somewhat unconfident.... only one that comes to mind is Keldeo.
Bennett: Genesect
Serra: Articuno, beautiful, yet deadly, since Serra was a model.
Luna: Uxie, embodiment of knowledge, who restores her broken memory
Samson: Terrakion, powerful, yet just and a nice guy all around
Ciel: Either a legendary bird or a Force of Nature
Terra: Groudon so she can rampage and smash everything duh
Charolette: Ho-oh...Burned tower, her house Burned down, eh, eh? I'm probably just rambling at this point. I'm tired.
Saphira: Kyruem or Rayquaza, both are strong, unrelenting figures
Laura: Shaymin
El: Arceus, duh.
I'm just listing off named characters btw. Feel free to turn down any of these.