If you take the elevator from the Zhent Mercenary's hidden base it brings you out on a ledge with a rope ladder. There are some wooden boxes in front of that need to be climbed over, so I just kept the rest of my party back and used Lae'Zel with a bow to whittle them down a bit, I think there is some path-finding issues with these guys because the trick is to make a ranged attack and then climb back over the boxes in the same turn. They get stuck in their decision phase on their turn and won't do anything. They -do- break out of this eventually and will try and jump up the ledge, so at that point make sure your party is spread out, my party was Main Cleric, Shadowheart, Astarion and Lae'zel. I considered Gale or Wyll, but I find they are very squishy, and at level 4 extra damage isn't really so great over survivability.
