if you want to take the room with the undead dragon in really easy..you can run in quick so they spawn then run out..then stand by the gate lever and open it shot a spell and it will close, open shoot spell close
This is exactly how I did it on my level 1 playthrough. Not sporting, but hey, I was level 1!
For a normal playthrough, since the place is crawling with undead, fire works well and a few flame atronachs work wonders to clear things pretty quickly. For the priest, if you are preparing, bring shock + magic resist, he does almost all shock damage with those bolts.