So my final team is this:

Kain Lv 63, 4405HP, and he has the Holy Lance
Rydia Lv 57, 2089HP, and she has the Fire Whip
Yang Lv 61, 6202HP, and he has on R.Hand Hand of the Gods, and on his L.Hand he has Cat Claw
Rosa Lv 60, 3211HP, and she has Rune Staff
Cecil Lv 62, 4645HP, with Excalibur, and he wears a whole bunch of Crystal gear.

I keep losing to the horrible Big Bang attack - I'm sure if I navigate a way round it, I'll be alright.

Give me help plz.