Yep, did that on my last playthrough - if you know what to expect, it's ok. I waited until they had some distance between them, attacked them first, and then forced them to waste turns getting to me, and...as always... occupied the high ground. I took out the blood sage first. I didn't even need to do anything very cheesy - but I was on full strength and knew exactly what to expect. I think if your party was surprised by all of them, and they got attacks in first, things would not go well...That is what bothers me, a lot of encounters are winnable because it is easy to sneak about (or in this case just walk about) and get to attack first, fairly consistently.