If it's not the SNES version, you should have some of the items that work as Wall/Reflect -- Lunar Curtain, is it? Have as many people as possible use those, in addition to Rosa's spell. And have Kain Jump -- even if he doesn't have a wall up, if he's in the air, nothing will hit him anyway. Let Rosa go first and heal everybody a bit (they'll need it, since MegaFlare/MegaFire is the first thing they're hit with), then start keeping the walls up. Keep having Rydia use Bahamut, and if you can, have Cecil/Edge with Berserk and/or Haste (those items are Bacchus' Cider and Hermes' Sandals, respectively).

If Edge has both of his final katanas, one of them -- test it out, I can't remember if it's the Murasame or the Masamune -- can be "used" as an item on himself to cast Haste. I don't believe he can use it on any other character, and one of them cast Protect instead -- and I'm not sure whether or not they reflect, but I don't believe so -- but it might help save him a turn so he can get to throwing things (this battle would be a good one to use the Spoon/Knife that Yang's wife gives you) or hammering away.

I still think they should have kept some of the old names -- White, Nuke, etc.