Xavier 's castle is briefly seen (from an outside view) at the beginning of 2.16 in the background. It looks very similar to Eric's castle. And from the inside, they look almost exactly the same (except the different colors and decor). So is Eric a descendent of Xavier or maybe one Henry's older brothers (after all he and Cora were fifth in line to rule). I doubt Xavier got over throne by a neighboring enemy (maybe Eric's dad), because Cora made Xavier super rich. He could afford as many weapons, soldiers, catapults, rations, etc. he wanted.
You're probably right, but I still live my theory. it would explain how Snow was found by those two soldiers so easily. Regina would be familiar with the area Snow was hiding at because she (Regina) was born and raised there.