This chapter is totally confusing..
First go chess to show girl is not growing up, pretty boi wants to do some NTR, MAMA KWEEN say OBEY.
Uh-huh I totally get it. /s
If the dukedom has been conferred due to royal ties (e.g. brother of the king) then the children titles are going to be prince/princess.
If the dukedom comes from merit, then it's going to be lord <name> or lady <name>.