I have a lot of trio group ideas of mismatching for some fun dynamics among this insane cast.
Terra, Axel, Riku: A big bro squad would be fun.
Aqua, Axel, Isa: Mainly because Aqua and Axel would have a fun dynamic, and Isa can break them up when they argue.
Kairi, Xion, Ava (or Aqua): I didn't get to see Kairi and Xion interact in KH3 sadly. This would be the girl team. And since I'm secretly holding out that Ava is a green haired Kairi it could be a Kairi squad. But if not Ava, Aqua could play the role of leader of this group.
Roxas, Terra, Riku: Powerhouse team, and see a rivalry between Riku and Roxas while Terra is confused about their history.
Sora, Roxas, Xion: Got a little of this in KH3 but I want more of this yummy Soraverse.
Ventus, Lea, Isa: Old friends going on a adventure or something.
Roxas, Xion, Isa: A truly awkward group as Isa is with the two kids he tormented. Would add a lot of growth for all of them to interact, and would shock Lea to see them all together.
Riku, Isa, Terra: Former jerk squad, bonding over how they use to be jerks via jealousy, darkness, or some other crap. They could play off one another to become better people for their loved ones. Though Terra wasn't a jerk.
Roxas, Donald, and Goofy: Donald and Goofy going on a adventure with Sora's Nobody.
Xion, Donald, and Goofy: Same as with Roxas. Donald and Goofy would feel nostalgia for her Kingdom Key.
Sora, Ventus, Roxas: I just feel this one has to happen for obvious reasons. Not much to say on it though.
Kairi, Roxas, Xion: A team that forms whenever Kairi goes to Twilight Town on her own. Kairi and Xion can go shopping and seashell hunting, forcing Roxas to carry their loot.
Namine, Merlin, Fairy Godmother: A magic squad helping everyone behind the scenes.
Luxord, Demyx, another reformed Org member: Luxord and Demyx have been showing a good guy side since Days and KH3 delivered. Just put another reformed Org member with them and they can form a trio that helps Sora too.
Terra, Aced, Aeleus: Physical powerhouse team squad.
Edit: I just realized I switch between calling Axel/Lea. How annoying XD