He’s a successor, what kind of logic is abusing a successor who will soon have all the power to do whatever he wants with you
Actually he's just a successor in name. The reason why they're so pressed in marrying Karhan off is that when he gets married they will suck money up from the bride and get back the eldest son to inherit the dukedom. Karhanis the one being married off to the FLs family in this situation. He will not have the right to carry the last name of their family because of that and he will be politically removed from the household.
Well that sucks. Also weird, cause doesn’t marriage usually solidify the position of the heir? Like in royal family
In this case he wasn't written as an official heir. Coz if you notice he wasn't publicly introduced in a ball or he didn't have an official audience with the emperor to be recognized as heir. So Karhan is pretty much in same situation as a daughter who is gonna be married away.
Which wouldn't solidify anything since he is replaceable any moment on especially when the eldest son return from exile.
DISOWN. DISOWN THAT OLD HAG