Each House has a council of its own that makes decisions for it, and the original families that bear the names of the Houses as a family name may have prominent positions within their House, but those that we see are not directly in control of House business. The Houses’ nature as clans also means that they are families, although it’s not exactly necessary for the original families to necessarily hold power within the Houses. Perhaps the best way to describe Resdayn and later Morrowind is as a federation, or federal state? This is also telling in that House Telvanni didn’t join the Ebonheart Pact, and wasn’t compelled to do so by any central authority. Despite a terrible description of them as “political parties” in the book Great Houses of Morrowind, I see them as to function more like self-contained states, with each maintaining a military, independent infrastructures for worship, learning, trading and several other functions.
The Great Houses evolved from clans that banded together for mutual protection and support, and, possibly still function as families in some way, if you believe Councilor Lleril Morvay. Subscribe: Anchor | Apple Podcasts | CastBox | Spotify