If you put Edgar and Sabin together, they'll own, but you'll be wanting some healing.

Locke and Terra and Celes will also reap havoc.

Cyan and Gau are pretty tough, but you'll wish that Celes was on their team too.

The big decision is whether you give Celes to Cyan and Gau (Who need it more for finishing since Gau probably isn't very powerful yet) or whtehr you give her to Terra and Locke (Because you might want to have Locke steal tonics. Also, they are capable of being defeated faster without a 3rd.)

That's my experience. But really, that was a pretty hard part of the game, if I remember it accurately.