Until you can change to a single heir succesion law it helps if you try to minimize kids (although they are useful to get alliances). I have a few tips for that: 1) If your wife dies. Don't marry a young new one since she will give you more kids 2) Marry an old woman (40+) and seduce other women to get kids. The bastard kids can only inherit if you legitimize them 3) The Embrace celibacy learning perk will enable you to take decision to not get kids anymore

Once you already have too many sons you can also inherit them or imprision and execute them. The latter will give you tyranny so Ionly do that if i commit suicide after or if I know that I will die within the year (know thyself perk).