you're more than good enough to kill Ubers.
Just let Hephaesto tank everything. Don't try to face tank them. Use Lethargy Sigil on them all.
For Izzy and Baal, make sure to stand BEHIND Hephaesto so he's between you and them. Easy setup for this is to just teleport nearby, do not move, and give Heph a second to charge them. Then just ES them without moving from that spot. Reposition if Baal teleports before you get Sigil on him.
Sometimes Heph won't go straight at them, going slightly off the path because of a different monster or something like that, so just make sure he's face tanking the Ice Bolts before you all out attack.
He can face tank the Ice Bolt reflects effortlessly, while they will melt you. Alternatively, you could pop some Thawing potions and put on a Ravenfrost ring and you'll take far less damage from them.
Never fight Baal and Meph at the same time. The conviction will melt you if a stray Ice Bolt hits you or Baal teleports on top of you. So always lure Meph out to take on alone. Diablo can't do anything to you.