It depends on how you play the characters. My current game, my first King is still alive... so there isn't a reason to start any revolts yet. And I also circumvent this by giving my first born son the heir to the titles in question, while other titles go to the other sons. The second son is king of Burgundy, while the third is of Bohemia, the fourth of Frisia, fifth of Poland, sixth of Lithuania, seventh of Bavaria, eighth of Frisia... meanwhile two of his sons rule kingdoms outside my realm. (Sweden and Carpathia respectively).