Ah... I used to love the challenge of Ultima. Now I propose a challenge to you. Do it without Aura, Meltdown, GF's and invincibility techniques. It is extremely hard but it can be done.
Here's a way you can do it.
If you can manage to get either 300 Ultima's or 300 Holies beforehand (the hidden Ultima Draw Point at Shumi Villages costs 5000 Gil to use but it gives 7-9 most times) then Junction them to Str or Vit. Have everyone at Lvl 100 also (although the HP's of Ultima and Omega as a result are much higher it helps for stats). Now I use Zell, Irvine and Squall, mainly because of their natural high strength (if you can't get the 300 Ultima's or Holies (something around the 190-220 for Str should do.)) and I also Junction Triple to Spd for all three. You would have drawn this from Cerberus at Galbadia.
All you need have on you other than that is strongest weapons, some Full-lifes or Lifes if nothing else, Haste and a bit of luck. I did it in around 30-35 minutes.
If you try it, I wish you the very best of luck
