Killing all the Haunts?!?
Well, calm down. Haunts are the nice laughing Skeleton guys with the chains and the swords. They can be backstabbed, or blown up with fire arrows and mines, or flashed to death. Keep 1 last fire arrow for the last task. If you think you’ve killed them all, but Murus still wants you to kill them all, then you’ve most probably missed the one in the alchemist’s cellar. Have another, closer look at the winter tunnels.