Sounds like you're lacking DPS. Focus on making the fight as short as possible. Fights that stall are never going to be any good.
We just DPS the crap out of the mob and fight through it.
If push comes to shove, when you're just about out of mana and the mob's almost dead anyway, pop reinforcement. Don't need mana to hold aggro then, and by the time reinforcement is off, the mob should be dead.
If members of your group are dying because they're being stupid, you can't solve that

- but, if you have a healer worth a damn it shouldn't be a problem. Sentry watch might come in handy for you on this fight when you see people about to die...
But yeah, focus on killing as fast as possible to lessen problems.