You know what, I have the perfect solution. Just find a guy who is into cuckolding to be king. That way, whenever the queen gets frisky with another fella, he'll just quietly jerk off in the corner while they do it, and the kingdom itself will stay rock solid instead of collapsing into an anarchic mess.
Now, I know what you're going to say next. Succession laws are holy and must be abided by at all costs or some such. Well, in practice, anyone with a halfway justifiable claim to the throne and a few thousand guys with swords ("I have more guys with swords than the other guy" is itself very much an acceptable claim) can have a crack at seizing the throne. Not to mention, with the consent of a majority of the most powerful vassals, succession laws can be changed, just like any other law. So, I say we find some poor, spineless bastard with a small penis, give him a bunch of guys with swords and have him take the throne. Then he can change the law to say that any heir who is not turned on by his wife being reamed by another guy (preferrably a black guy with a much bigger doodle than the husband (not that that's a difficult bar to clear)) is immediately disqualified from the line of succession without question.
There you go. You'll have a kingdom that can stand the test of time, or at the very least the test of Jerome, Leroy and Tyrell running a train on the queen. This, by Jacob's own admission is something that his kingdom cannot endure without collapse, meaning this particular design is objectively stronger, more stable and is all around a superiour government to yours.