Yes but WHY did it say that he was the heir? I didn't do anything because it said he was the heir. So if I had died first instead of my wife, would he have become Emperor?
It's not consistent. That's what I'm saying.
I take it when he was despot of italy, he was also your vassal but is no longer as ruler of russia?
if that is the case and he is no longer your vassal, your other child with BiP will succeed first.
Giving any kind of title to your progeny will increase their standing and dynastic position. Thus making your first born son without the BiP trait the italian despot under byzantine rule, qualifies him to supercede his younger brother with the BiP. However since he no longer is a vassal of the byzantine empire as russian emperor, he no longer gains favourable standing and dynastic privilege. Thus if he isn't your vassal, he'll be skipped for the younger son WITH BiP.
Normaly in elective monarchy it is impossible to elect your grandson if their father is still alive. You can bypass this by granting any title to the grandson that is higher than the fathers. (father is duke, you give grandson a kingdom)