Curious to hear your experience with the scenario on a few points:
I've had a hard enough time coming out of each generation with one viable male heir, so the gavelkind thing hasn't even come up yet.
the first king, Alfonso? married, had a daughter, his wife promptly died at like 20, he remarried, they had a son and Alfonso died, as he was fated to, at 40. Then I was playing as an infant with some regent who will not agree to anything I wanna do. That kid has the trait "inbred" for some reason I couldn't puzzle out. He became infirm at 4 and died at 6.
His half-sister inherited everything, she married and had a daughter and a son and then died almost immediately after the birth of the son at like 24. It said it was pneumonia I think, but is there a chance it was foul play? She got vaguely "Ill", it cleared up, then it came back and killed her. Now I'm playing as an infant again, again with a regent who won't approve my plans, which by now have turned to the smaller muslim kingdoms to the south.
Is this just a run of bad luck? Sounds like the births played out pretty differently for you.
This idea of laws only applying to the primary title. On the "independent realms" map overlay, I'm controlling Leon, Castille, Navarre, and one of the smaller muslim kingdoms to the southeast (can't remember the name). But my borders surround all of that and when you zoom out it labels the whole thing "Leon". But anything in the law tab doesn't apply to most of that you're saying? I have no idea what the succession laws would be in the muslim kingdom for example. How do i find out? The only way to influence those is to destroy the de jure kingdom that's down there?
Destroying de jure titles to pass titles to just one son. Would I want to basically destroy all the kingdom-level titles except leon? Or would I need to also destroy duchies? Not sure if its possible to destroy counties, thats kind of the games indivisible unit of territory right?
territory acquisition by marriage. How exactly would this happen? Right now I've got one son and one daughter. If I married the son to a princess, she's probably not gonna stand to inherit anything in her part of the world, but for the sake of argument lets say she will like inherit a duchy. Will it become like her duchy with her as my vassal? Will it be part of my "realm"? What do I do with the daughter? I was thinking about trying to marry her into the Galicia rulers, but first of all they're 1st cousins so that might be genetically dicey. Secondly I don't quite see what that would do for me. Her husband would just go on to be king and that doesn't really help my prestige or titles or land right? They would be from the same dynasty (House Jimena), so maybe some prestige points come from the prestige level of your house?