



Confused about how this succession works
Hello,
So my current player character, King Hermenegildo of Leon is going to die soon. I decided to designate my 2nd oldest son Guillen as my co-monarch, because I wanted him to be my player heir (I have Absolute Crown Authority).
My previous player heir was Hermenegildo II because of primogeniture, being my oldest son (in the 2nd picture), but he caught the bubonic plague and then died. I assumed that because of primogeniture, Guillen was sure to become my player heir along with the fact that he has co-monarch status.
Now for some reason, it turns out my player heir is not Guillen, but Hermenegildo III (in the 3rd image), my grandson and the first-born son of Hermenegildo II (who caught the bubonic plague and died). The line of succession also confuses me because my 2nd in line is my great-grandson Gonzalo, son of my player heir Hermeneglido III, and then Guillen is 3rd in line.
In the 4th image, I circled all my sons who I assumed would be in the line of succession before my grandsons. All my sons are older than my grandson Hermenegildo III as well.
I can't designate my heir because it says that my co-ruler (AKA Guillen) would be my heir, but that's not the case.
I haven't disinherited any of my sons.