it's explained in the novel later, there's quite a bit of politics in this story
*SPOILERS* but i'll be as vague as possible
Basically there is a sickness in the Imperial family, when those high in power get too sick they are stripped of the right to the throne but still take the Imperial name as a consolation.
Quotes from the novel ch 198
"The first 'La Orr' surname was a grand gift an Emperor gave to his beloved but power-hungry Prince. "
"Yet, even excluding the Princes and Emperors who became Dukes while bearing the surname 'La Orr', many princes and emperors died mysteriously young, one after the other. "
Basically being a La Orr Duke means he no longer has the right to the throne. Even if now he *spoiler* *spoiler* *spoiler* ( i don't want to say it lol )
Ohhh thank you very much, now I can understand it!
When they introduced Kishiar, they said because he is the emperor’s brother he had to give up any claim to the throne. That’s why he is the duke, but got to keep the last name out of respect.
Now there is another guy with the same last name, no one forced him anything and he gets to be the crown prince? Wtf??
Shouldn’t brother or a child had the rightful claim for the position instead of a cousin or whatever that guy is?