This quest can be completed as in Stemming the Skeletal Tide by repeatedly entering the Underworld and capturing the first Skeleton of Dhuum that walks near the starting area, although that would be expensive. Alternatively, most Underworld solo-farming builds can be used to capture all three required Skeletons in a single run, with the drawback that you must wait 1 minute between captures due to the Weakened by Dhuum effect. There are at least 5 Skeletons that you can access without taking the Clear the Chamber quest to open the doors.