Yeah, him using Meteo is a really really bad thing, I haven't been able to survive one honestly
now, as for the question, get Kain jumping, if hes in the air, he cant get hurt as easily as the others, also, try to keep all your characters alive, have plenty of Phoe Downs, because no matter how high my rosa is and even is she is sitting in the back row, shes still pretty much an open target, and when you dont use the white mage twin, who is also pretty much a sitting target, it becomes hard to keep your party healed, so, try your best to keep all healed up, Cure 4 works great, elixers are helpful, but not really needed, buy lots of Fuma Shrikens, have Rydia (when shes alive) and Cecil flop back and forth between attacking and helping the healing via X-Potions and Phoe Downs, because likely, Rydia and Rosa will likely be killed, so, Cecil will be the one tanking a lot of Zeromus's blows. Edge, with how awesome he is, still is nothing compared to Zeromus's attacks, and I really suggest if he dies, keep it that way, he will only waste MP and Phoe Downs.