I have some ideas concerning various Dunmer things:
One, treat the Ashlander tribes as titular duchies, not noble houses (not actual tribal titles, because those get destroyed when a duchy is made). I think the tribes are important enough to the Ashlander identity (especially as they are mentioned in the Nerevarine prophecies) and distinct enough that they shouldn't be so easily destroyed as families are. Furthermore, by the time of TES III, none of the Ashlander Ashkhans actually bear the name of their tribe.
Two, rearrange the holdings of the Ashlanders a bit. I would suggest the counties they hold be divided as such: Urshilaku: Ashlands, Ahemussa: Grazelands, Erabenimsun: Molag Mar, and Zainab: Zafirbel. Given the county positions in EK, I think that's the best that can be done to accurately represent their holdings.
Three, include the Ordinators and Buoyant Armigers as vassal Holy Orders to the Tribunal Temple, or the Kingdom of Morrowind if the Temple is destroyed as a landed title. I'm not sure how feasible it is to make that transition, possibly via events? Could be a reason to hold off on it.
Four: Change the name of the "Velothian Empire" to something more lore-accurate, like simply "Empire of Resdayn" or "Empire of Morrowind". I know those are the kingdom names, but the area including both the mainland and Vvardenfell has usually been know by one of the two, and "Velothian Empire" just seems artificial.
Thanks for taking the time to read it, and I hope this is helpful.
Well, the Ashlander tribes seem to work as a clan, from which the base is a family, so it's not that inaccurate. The "royal house" bearing the name of the tribe is just a matter of convenience, they could have any name, and be any tribe.
Sure, I'll look into rearranging it. Although I warn that it's unlickely that I'll give Zarfibel to the Temple (Also, bear in mind that their 3rd Era holdings may not correspond to their 2nd Era ones)
The Buouyant Armingers are already a vassal Holy Order of the Temple. The Ordinators, for the time being, are the name for the Dunmer retinues. This may change of course.
As for the Velothian Empire, I like the ring on it, if you personally don't like it it's a very easy modding, just look for the Empires file in the localisation folder and change e_dunmer;Velothian Empire... to something else. Of course, you can always change the name in-game trough title editor.
You're welcome, I hope my answer proved helpful ^^