I think in a way they are Fergie's kids after all. Basically they could fade into a privileged private life and live happily ever after, turning up for major events (jubilee, coronations, ....). But I think they like the publicity and they can't do without.
So they use what they use best: topic kids (and you get to see these cryptic "not showing my baby in the pictures I am sharing" - but they seem to be trendy at the moment with a lot of young moms, so maybe they are developping a fan base there. I am friends with a good few young mothers on Insta (most of them are my former students) and there are heaps of baby pictures posted daily, they basically only show the baby, but the babies face is covered with a smilie or something like that - so you get to see two hands or similar things and you wonder: Eh ... what does this picture tell me?
Bea and Eugenie are the only sister + sister pair of her generation (H+W = 2x male, L+J = mixed, Z+P = mixed) so they are looking for some publicity there.
There is a very different approach between Beatrice and Eugenie. Beatrice does NOT post on social media and is only seen when attending the major royal events or when the media find her at a social event such as going out to dinner.
Eugenie posts regularly on social media but not Beatrice. Even Edo has reduced his posts on social media limiting them now to wishing his wife a happy birthday and presumably he will post again on Sienna's birthday.
The girls are very different in seeking publicity as Beatrice does not actively seek it at all. I do realise that many people think she shouldn't even have a life by doing things like going to music festivals or out to dinner where the media will see her and report her attendance, as they do many other celebrities.
Maria - sorry I have no idea how to do multiple quotes in the one post. I have tried but find it is beyond my limited computer skills.