Co-op can be done with any number up to 4 players.
Just bear in mind though that the game only has 2 "difficulty" modes. One for single player, and one for co-op in which enemies have much more health. a 2 player Co-op run would be quite a bit slower than a 4 player one just because bosses would take much more time.
Also note that 2 player coop is a lot slower than single player. In single player, you're not bound by the character's walking speed, since Mog is a thing.
I thought the coop scaling changed at 1, 2 and 3 players (with 4 being identical to 3?). MLSTRM probably knows more about it than I do though, so I'll trust his word on that.
If for whatever reason you did do a two player run, the optimal team is probably Any% character of your choice and a Yuke.
I'm very late posting this, but I wanted to share Wobmiar's awesome Any% TAS of FFCC using all of the newest glitches. Please check it out!