I heard about these guys in Oblivion based on the character http://elderscrolls.wikia.com/wiki/Greywyn_Blenwyth with the Vile Lair.
I think it would have been cool to join a vampire coven or vampire faction like this in Oblivion. They had several vampire factions you could join in Morrowind and in the Dawngaurd dlc with Skyrim. These guys seemed really interesting how they served Sithis and the Black Hand in their own way. svcks they were all killed though. Seems most vampire covens made easy targets in Cyrodil or just warranted vampires a death warrant for being in one.
Why does Sithis hate vampires anyway?