Why are the Twilight kids the only quartet friend group, while the others are trios? Also, why are the roles/archetypes of each member in the groups so similar and blatantly obvious lol

Three things.

One, you put Roxas in two groups here: the Twilight Town group and the Organization group. He's only supposed to be in one.

Two, even without Roxas the Twilight Town kids don't fit that structure at all. Pence is the smart one, Hayner is both the Main one (as the only one with any fighting skill) and the Tall/Edgy one.

Three, Ven isn't "the main one" of his trio either. Aqua is, while also being a girl. Arguably Ven's got a gender-swapped version of the same position Kairi occupies. We only think he's the main one cuz he's one of the Sortas (but then Xion also qualifies), but Aqua's got two extra chapters dedicated to her and the lead position in her own game.

/r/KingdomHearts Thread Link - i.redd.it