What advanced class are you? And which skill tree in that class?
If you are DPS and using your healer, you shouldn't have a problem. I can't remember the quest as I did it over a year ago.
Also what are the mobs? 2 gold, 2 silver?
And make sure you use your concussion missile on any gold first, then take out the other.
Merc with all points in assault. No mob in the fight with the "boss"