Even the amount of pre-written stuff for Crusader Kings is insane.
I once got seduced and murdered by my own sister as revenge for murdering my brothers to inherit their kingdoms. The funny part was that the “getting seduced by my sister” part was apparently a scripted event based on actual history. And that’s just one example.
That sounds like the north Iberia start, with the 3 brothers each with their own kingdoms and the intrigue sister.