The only way I was able to fix it was by reloading and advancing more aggressively, so that they would call for reinforcements. When that happens, the soldiers will open the door from the other end, giving you access. Barring that, I couldn't see any other entrances that might help. I focused attack on the melee fighters first, leading them back away from the archers where I could pick them off, then coming after the archers with the last one by the door. Keeping the last one by the door should ensure that you're able to alert the rest.
I wanted to do that, but there's no one left to kill. The only person there is one single highwayman who I can't target or interact with in any way. He just paces. Da fuq EA?
Don't use necromancy spells there and disable them on your party spellcasters tactics (Dorian can resurrect dead mobs to fight on your side).
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