After act 1 I had to set difficulty to explorer for most fights unfortunately, so I don't remember the difficulty setting for this particular fight.
Your worst enemies are the leader (the orc) and the two spell casters, so focus on taking those down asap. Use area spells, especially spells that create difficult terrain, that will slow their progress. Hunger of Hafar spell as has been said is particularly nasty, you probably cannot avoid being hit by that at least once. I like to cast haste on a warrior type companion if I have the opportunity but there are probably other ways to do it. A well placed fireball can take down several archers at once, in the back. I leave the archers above to the harpers, or take them down last, as they are not the greatest threat.
