I'm not in the situation yet, but once i have kids I'll tell my parents that, if i ever see a picture of my kids in any of those bs platforms (fb, Whatsapp..) they'll never get another picture. parents have the ultimate decision about such things, if somebody else doesn't respect your decision, they need to live with the consequences.
it might sound harsh, but seems to be the only really working strategy. i gave up explaining them stuff over a decade ago.