Question:

Can two people be dukes of the same area at the same time?

For example

I have Person A ruling as the current regent of the land, so he’s technically the “King”, but before this he was the Duke of a smaller area

Is he still the Duke or does he have to give up that title to become King?

However, Person B (ignoring a whole bunch of backstory/plot twist shenanigans) is named as the heir of Person A’s duchy, who is currently alive and ruling as a King

Does Person B automatically inherit Person A’s duchy, since Person A is a King, and therefore Person B can be called the “Duke of ThisLand” even though Person A is still alive, or does Person B have to wait til Person A kicks the bucket before he can be called Duke?

And finally, as an unrelated question, if Person B becomes engaged to Person C, who is a Princess, does Person B gain the title of/can he be called a Prince as well, or does Person B have to wait til he puts a ring on it officially to be called Prince?