Question about feudal duties; in medieval Europe lords could hold letters patent from 2 sovereigns i.e. Norman lords as vassals to the king of France via the duchy of Normandy while simultaneously holding lordships in England. Are there any examples of this in asoiaf? Perhaps in marches or the like. And if so how does one determine which oath to hold? Does it come down to simple pragmatism and financial considerations? Thanks Steven! Also, do you have patreon account? I would happily contribute!

Good questions!

1. I can’t think of any in ASOIAF, I think GRRM deliberately avoided that situation in order to keep things simple, similar to only using Lord as a title. 
2. It’s a complicated question of both politics (as you suggest) and law – which title came first (so how free were you to make additional oaths), whether the law of either country recognizes titles in other countries or allows for lords to be vassals to two monarchs, etc.
3. I don’t have a Patreon…yet. I’m waiting until the major rewards from the Kickstarter I did have been sent out before starting any new crowdfunding project.