Greetings and salutations!

So, I've been sifting through the forums, but haven't had much success finding member's opinions and theories on certain questions I have concerning these three. Now, it has been some time since I have played Morrowind, so forgive me if the answers are in plain sight.

Anyway, I was curious about how simultaneous membership in the Morag Tong and a Great House works. I realize that you are able to do so in-game (at least, that's what I remember...), but how would it play out in terms of lore? Are members of the Morag Tong also allowed to be a member of a Great House? If so, what happens if they are given a contract that marks someone within their own Great House? If I recall correctly, I believe guild members were allowed to decline particular contracts, but my memory is a little fuzzy.

As for my next question, does anyone have theories or sources as to what Hermaeus Mora's relation to the Morag Tong actually is? Besides being the "sibling" of Mephala? Also, while I'm asking this, how about Sanguine's relation to the Morag Tong/Mephala, concerning the Threads of the Webspinner?