I have a small issue. Not with your mod, but I think with the heir system, but well, let me explain...
I'm playing Lithuania. My king, who is a Regent, had a son quickly. His son became the next heir. Then, I accepted a man-of-the-day who became adopted son of the heir. The heir had a son pretty late and he came of age when the regent was 80.
So at this time, the regent is 80, his heir (his only son) is 43, he has an adopted (MOTD) son who is 41 and a biological son who is 16. The biological son has had the Heir Crown since he came of age. Before that, the crown was on another family member who has nothing to do with all the story.
So logically, when the regent dies (he's the FL, not the FH, so the next heir should be the one with highest authority), the next heir should be the 16 years old biological son, right ?
The regent died of old age next turn ; and the heir is... The 41 years-old adopted son ?!
Well, no worries I said, I created a "NotHeirYet" trait which gave -10 authority and gave it to the adopted son after reloading before regent's death. Same issue. Tried to mod the heir crown for it to give +80 auth instead of +8, same issue. Now I think I'm gonna kill this adopted son but I would like to understand why he become heir, so if you have any idea, you're welcome.