[@TheRedWatcher] I like the idea but I would rather the Frozen Tears be firmly in one place. As much as this is based on feudal politics, I still have PTSD back when I was trying to wrap my head around the weirdness that was the King of England holding land inside France but as a vassal of the French King despite also being completely independent. 

I do have another proposal though, what if instead of being geographically split between Frostmark and Mistland, you're politically split? Like what if you're married to a Mistland princess and thus are bound by alliance to the Mistland but BC's House still rules over you as liege lords meaning you owe loyalty to two different people who might one day want two different things sort of like Brandenburg-Prussia.