Does anyone know to which house each of the Tribunal belonged before their ascension?

Thanks

Sotha Sil was from the minor Dunmer house of Sotha, but thats all that I know of. Given Alemexia was Nervar's wife, I would place my bet that she was a member of House Indoril as well, though one might argue Dres given where Mournhold is located. Vivec on the other hand I have no speculations on.

If the Sermons are any indication, Vivec was common born. I'd also say that Almalexia was originally Indoril, and that Nerevar married into the house (an old dev post has him originating from the minor house Mora). The Sermons have him as a caravan guard, and that's not a position I'd expect someone from Indoril to hold.