The poster I quoted said this:
The princesses I mentioned are not the daughters of the reigning monarch (Elizabeth) or the granddaughter of the male in line (Charles). Unless they mean any male in line for the thrown, Beatrice and Eugenie do not meet these standards. If the poster did mean ANY male in line for the thrown, we would have many more princesses running around as the succession rules go pretty far out there.
They are granddaughters in the male line though - through their father. It is any male. They don't actually have that many as it stops after that generation. So (had they been boys), their daugther's wouldn't be Princess, since their daugthers wouldn't be the granddaughter of a reigning Monarc (assuming there isn't a whole lot of deaths in the family).