Stuck on this quest, then these hints will help you!
Quest: Haunted House
You need to find an NPC in the corthiard and interact with it.
This will move the plot further.
But Beware: This side-quest is bugged anyway. You cannot proceed after (spoilers!) an ambush. Maybe I got softlocked because initially I escaped back in the basement and basically started the encounter twice.
My advice to possibly avoid getting softlocked — try not to retreat and exit the map.