Maybe try to persuade your granddaughter’s parents that you are really not comfortable with Facebook for reasons of principle (or whatever) and ask if they could perhaps also post the pictures elsewhere or use one of the other myriad ways of sharing available in today’s digitally connected world? (And you did say “one of the main ways” implying you do have others.)
Not addressed to you directly, but in general people do need to be persuaded to make some minor amount of effort to avoid FB. But the digital age monopolists know that inertia selling is very compelling. Inertia selling never reflects well on the inert.
