The Ancient Skeleton, Heddad the Thief wants you to arrange for the burial of the corpse of his brother, Haddan the Thief, next to him in the Crypt of Eldfell.
Approach Heddad in the Crypt of Eldfell. You need to listen to what he has to say; afterwards you can fight him, or proceed on the Quest he sends you on.
Upon killing Heddad, return to Valcherim the Blacksmith in Eldfell. He will give you 2500 gold and an enchanted suit of Golden Full Platemail, Armor 14, +10 Block, and your fame increases.
Otherwise, accept Heddad's quest. He will teleport you to where his brother is hanging. His brother's hanging corpse is immediately to your left. Step left and tap on the corpse; you'll find 300 gold pieces.
Once you have found the money, go back to the Undertaker and speak to him about the Burial, he will advise that it will take several (approx 3) days to take the body down and bury it next to Heddad. After 3 days return to the Undertaker to confirm this is done, then go back to the Crypt of Eldfell and report his brother is now buried next to him to complete the quest.