Ralvurahva is a tough boss but his HP isn’t high compared to your attacks at that point of the game.
Heal every turn
Let Dagger cast healing every turn. If no one is attacked then simply wait for a few seconds to find out who will Ralvurahva attack then cast cure. If you don’t want to waste time then heal all every turn.
Use the blood sword
If you have managed to get the blood sword from Treno then Steiner’s attacks will be very powerful at that point.
Cast protect on Marcus
Since Marcus will probably have weak accessories, casting protect on him using Dagger might be a good idea.
Attack using Marcus and Steiner
Let both Marcus and Steiner use their physical attacks. Taking down the boss won’t take much time that way. (See How to defeat Scarlet Hair in Final Fantasy 9?)
Steal the Mythril Fork
Since that’s a relatively easy boss to beat, you have the luxury to steal from him. Steal the Mythril Fork which is a weapon that can be used by Quina.
Equip the Madain’s Ring
If you managed to purchase the Madain’s Ring from the auction house in Treno then equip it, for it can help you absorb Ralvurahva’s Blizzara.
Revive Steiner first
If 2 party members died then revive Steiner first as his high Hp will probably help him take another hit without dying. This will give you more time to cure him. (See How To Win Final Fantasy 9 Card Game)
How to defeat Ralvurahva in Final Fantasy 9?
FINAL FANTASY IX – Ralvurahva Boss Fight | How to Beat Ralvuravha in FF9?