Interestingly, almost every ancestral tomb on Vvardenfell is also already assiciated with one of the Great Houses. But I agree that taking those as a basis would be a sensible place to start.If we assume that every Dunmer family that had any importance was a house itself, then the ancestral tombs of Vvardenfell (probably mainland Morrowind too) could give us an answer. I don’t know if there is a distinction between house/family in their culture though. Even if there is, it’s hard to tell where the boundary is between the two.