OK, this thing is kicking my rear end BAD...3 fireball spamming mobs, and the only defense I've got is a ward (which is self defeating because it just svcks my mana out rendering me incapable of doing any damage) or a potion (which only prevents 20% of the one-shot-kill fireballs they're tossing). Only thing I can figure is to spam fire atronochs, but these jerks heal themseleves, and it's DPS isn't enough to down even one.
Is there any way to beat this other than going to the Companions and becoming a werewolf to rip those fireball spammers up, or spending a zillion gold to powerskill enchanting, find a fire resist item, and win that way?
My mage is on Expert with only 100 HP. I had the same problem you had, and actually it was even harder because in a necromancer with no perks in Atronachs. My winning strategy was thus, as soon as the first guy runs away I ran up and cast two Storm Atronachs on the corner he was standing on, charging up to this point allows you safety and your Atronachs can fight better. Then let them duke it out with the approaching Dremora, occasionally had to recast an atronach. Make sure you stay back from your Atronachs because the main guy will cast Chain Lightning and if you're too close it will jump to you. If you keep this up your Atronachs should get a kill or two and for whatever reason once the first Dremora dies the other should de agro and the main guy will run back to the end of the dungeon. From there its easier because you'll only fight one at a time.