Try using Irvine's Shot - good ammo is essential (but not Scatter SHot). GF? Use Cerberus and then use magics which only damage one opponent aka not Tornado, Meteor and Ultima. Use Zell's Duel - but dont use Burning Rave as it attacks all opponents - the other finishers are fine. Use Flare if you have any (Triple Flare is even better and if you have Expend-3x1, you have the potential of having 300 Flares per person - very handy!)

Make sure that you have learnt Recover (Leviathan) and get someone to junction it - you can use that to heal Rinoa and your party to full health without using precious magic or potions.