The uber bosses are easy... here is a quick run down of wtf you need to do.

1. Collect the key's (you need three sets)
2. Open all the portals in act 5 in the same game. (this assures you don't get a duplicate)
3. Open uber trist and run away as fast as you can. You need to seperate the bosses.
what we did was mephisto top left, diablo bottom, izzy? to the right
4. Mephisto will be much harder the lilith the other 2 are jokes.

If you have full confidence in your zealot just charge in there and smite the bitches dead, my smiter could take all three uber's without lossing any life. I of course had all the best gear but, /shrug... ive seen lesser geared players do it.