What you get is random - getting two bosses together is bad luck. I got this once in many tries and killed them both but I was level 8 and both my characters were melee - that makes a difference. Even so it took a bunch of potions.
Come back later if you want to bother - by then the quest reward will be trivial to you but most of us like to finish all we can even if we don't need the xp.
