You can tell by the way they address themselves.
Kokuo uses the very rare and dated "watakushi" which whilst old, is very polite. Choumei thinks of himself as lucky and Isobu addresses himself using "boku" which suggests he's quite gentle-natured.
So those three.
Gyuki speaks in a pretty rude and arrogant manner and has a history of playing up. (Fukai anyone?)