just have squall rinoa and zell, 9999 health for each, 100 ultimas to thier elemental defense, legendary weapons, all the gfs you can possibly have, triple, aura, demi, use lots of limitbreakers (pray for lionheart,invincible moon, and wishing star) make sure you used a phoenix pinion in a previous battle and as many megaelixers as you can get (refine bahamut's card), max out everyone's stats.
i did that and the battle turned out to be quite easy. greiver's shockwave pulsar KO'd my whole party but luckily the phoenix saved me. those were my only ko's (aside from purposely koing the other three party members)