ok, I have some usefull info here. When you battle seymore try and get Yaua up to max Overdrive, then when he summons his Aeon use the Mega Summon overdrive manover, This enables you to select Shivra who is displayed as ????? then use her overdrive manouver straight away, which is Dimond Dust. This does a massive 9999Hp attack on him and then he uses pain to attack you. From here on in use Blk Magig to heal yourself by casting Blizzra on yourself. keepdoing this till you have another overdrive attack and then strike again with dimond dust. The Aeon should be dead now, then all you have to do is use Aeron to atack Seymore using his magic Break attack, Tidus on his Cheer manouver and Lulu on her Thundara, Fira, Blizzra and Watra attacks, Hopefully you should just about get through... If not remember to use Hi-Potions on all members at any possible moment. Hope this works!!
