my friend asked me why rupert and amir were still referred to as princes if they have their own kingdom so i went on a whole deep dive and here are my findings
typically princes tend to ascend to kings when the previous rulers abdicates or dies. lavinia and atossa are still very much alive as they are talked about in season 3 and from season 2 we know that they didn't abdicate because the kingdoms of the east and west are still standing.
however, you can still become a king if a prince creates his own kingdom which we see with the heartland yet they're still referred to as princes
i did more research and found a thing called a "principality" which is a territory governed by a prince. however, they're not solely based on size as there are some principalities bigger than kingdoms. so the other way a principality can be declared is by a higher power (such as a queen) granting the title and area.
so my personal headcanon is that with rupert and amir being barely 18, neither them nor their mothers wanted them to hold power as king especially with the heartland being brand new so they declared the heartland a principality and gave rupert and amir sovereign control.
(i'm aware that this was either just a detail that wasn't thought about in the making of the two princes or that they were declared kings after their wedding. i don't care this is MY headcanon and it keeps the continuity of "the two PRINCES")















