Succession issue

[RedBishop]

I'm playing with an agnatic-cognatic gavelkind kingdom and my brother inherited two of my counties, somehow his son and heir inherited a county on a different kingdom, I usually try to find arrange royal family brides for my sons, so I'm guessing that their kid inherited the county of the bride's father, anyway, now I'm getting the warning that I'm going to lose the 2 counties even when my brother has another kid now and I'd expect at least one of the counties to pass to the second son and to my realm. I even created a new duchy that contains the two counties trying to keep them in my control but I still keep the warning.
So I have several questions:
1. What's the inheritance rule that is causing me all this mess / why are his sons not staying as my vassals?
2. Is there any way to remove his titles without getting the opinion penalty with my other vassals? my control on the kingdom is a little thin right now.

 

[RagingJaws]

Shift to intrigue focus and spy on him, hoping to get a reason to imprison him. Hope the imprison fails, so he starts a rebellion solo. Win, imprison, revoke. Rinse and repeat. You could also fabricate a claim. Takes longer but gives you the chance to revoke right away, which your brother may bow to if you are much stronger than him.

As for them not staying your vassals, they already own land in another kingdom. So the title they inherit from your brother would go after their primary title, which is a vassal of another kingdom. The only way to avoid that would be either to give your brother a title that's higher than theirs, which makes the higher title under your vassal-liege relation primary, or pass a law disabling inheritance out of your kingdom (conclave law)

 

[Sfan]

1. There is no special inheritance rule that causes this mess. Gavelkind made it so your brother had counties, but this could perfectly be the count of tradadum instead of your brother with another succession law. What prevents this to happen is to have high crown authority, this avoids any county to flip away from your country during inheritances.
2. You probably have a claim if your brother had it out of a Gavelkind succession. I'm not sure if this requires a certain crown authority but if I'm not mistaken you can revoke titles freely if you have a claim. If you don't have a claim, fabricate one or murder your nephews until your brother inherits the county of his son. Then it's the opposite, you have a new county in your kingdom. But this may be pretty hard to find the 100% plot power needed.

Edit: I forgot the trick of the higher title but what RagingJaws says is 100% correct, this is a very easy way to do it.

 

[RedBishop]

The only way to avoid that would be either to give your brother a title that's higher than theirs, which makes the higher title under your vassal-liege relation primary, or pass a law disabling inheritance out of your kingdom (conclave law)

oooh If I give my brother the duchy he might stay? now I wish I wasn't playing Ironman so I could try this out . maybe I can make a copy of an Ironman save to test this out hahaha, haven't tried that yet.

 

[RedBishop]

As an update, I did give him the duchy but the warning didn't go away, since I wasn't sure if it was going to work, I focused learning and I rushed legalism 3 to get the law that forbids inheritance outside of the realm, unfortunately although I had a very long lived ruler, I also had 13 daughters and one (dead before succession) son, so now I have bigger problems on my hands. I'm calling this period of my history, the Romance of the 13 Maharanis, we'll see where this goes, thanks everybody.

 

[RagingJaws]

Sometimes the warning notification stays up even after the conditions are no longer valid. A minor annoyance but with more experience, you'll notice which ones are false positives and which aren't.