I started another game, but this time with a duke who sserved the king of Croatia. My character was quite old, in hes 50's I believe and he wasn't even married so I set my goal to marry, have atleast 2 kids and then aim for celibacy. I make this happen, I get 2 sons and a daughter. I proceed to capture many neighbouring provinces until it's just me, the king and he's daughter left.
My older sons traits were really bad, so I changed the royal law to Elective Monarchy. Everyone likes my younger son more, he gets all the votes.
Now I name myself the king of Croatia and everything goes to ****... Apparently when you "create" the kingdom, some of the laws change, so my older son claims the throne rather than my younger one, ofcourse I missed this or maybe there even wasn't a notification..
Now I don't even want to play..