I'm interested in participating.
According to the first post, you have no princesses yet?  I'm interested in playing as the older half-sister to the princes, the daughter of the king's first wife who died.  (Maybe the full sister of the crown prince [probably not; it looks like the queen mother would rather have both sons] and the half sister of the second prince?)  Or as the full-blooded sister.  Or as the king's sister's daughter.  I'm not picky.  And I would say whether my character is betrothed or not is up to the GM.
I also like family trees and would probably end up making one if involved.