Level up if you need to, but mostly just make sure that your Fighter has all of the ice equipment (including sword) equipped... The fight is extremely difficult, and you probably won't be able to keep everyone alive.

I can only assume you know that you should be flinging Ice-3s at his head with the Black Mage. I'd let the Monk just die when he dies, because you won't be able to heal everyone, and he's the worst of them, especially before you run out of Ice-3 castings.