How to defeat Ralvurahva in Final Fantasy 9?

Ralvurahva is a tough boss but his HP isn't high compared to your attacks at that point of the game. 

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.

If you have managed to get the blood sword from Treno then Steiner's attacks will be very powerful at that point.

Since Marcus will probably have weak accessories, casting protect on him using Dagger might be a good idea.

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?)

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.

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.

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)