mmm…if Henry sr. and Eva were brother and sister, according to what I got from “The queen is dead” (“the tiara was of my mother and of her mother before her”, etc…) , the kingdom passes from mother to daughter (because if it were inherited in the masculine line, then the royal tiara wouldn’t belong to Eva’s family but to Leopold’s), so, despite Hery being a prince, he couldn’t become an actual king, but a noble bannerman, lord of his own lands, etc…
Besides, if Henry sr. was Eva’s brother… how is it that he didn’t seem to remember Leopold in “The stable boy”? I mean, surely he would remember his sister’s husband. Even more, how is it that he agreed to marry his daughter to her uncle? how is it that Regina didn’t know her cousin? how is it that Eva didn’t visit her brother in all those years? sound strange to me…