I think he cross-dressed too. After the mother died there is a picture of little Roxant and Brill in male clothes and there is no reason why, Brill as a child should cross-dress as a boy.
I mean, its a patriarchal system so if they are girls it is more likely, that they will be married off to an other family and wont become the successor. (So girls will be less importent for the enemy -> wont be attacked)
I mean, its a big deal Leah will become the successor even through the Hildebrands are a womens family.
Kind of sad😒