yeah i tried this, and u cant win i dont think.
They get first go, and they completely destroy and annihilate u.
i had tidus, auron and yuna in my party
they are automatically in overdrive, so they unleash all their power on u.
the first one does this attack that does around 300k hp, then the middle one turns tidus to stone, and the little fat one does delta attack, which does about 1 million damage around, something like that.
I think u can keep tidus alive, becoz if u have a stone ward thing on then she might not pertify u.