I have elective gavelkind inheritance law. Apparently, one member of my Dynasty has an STRONG own kingdom and I can nominate him as a successor. I've bought succession support enough so he is a winner (he has 7 votes, the next best candidate - 6: https://i.imgur.com/FiIE9W8.jpg). But somehow, the heir is my step-brother, with 0 votes (https://i.imgur.com/pGfJQin.jpg). Why is it so and how can I make THAT KING to become my successor?
Maybe that's because I have Illegal controlled realm Inheritance? Should I just change that law? I'd try, but I play ironman and can't just try.