Sadly, non-technical members of my extended family do tend to use Windows and Facebook and there is very little I can do about it :-( There are some cousins who use Macs, so that's something. I don't think anyone but me uses Linux.
Twenty four years ago I set up the family@hoult.org mailing list, with about 50-60 people on it: my parents, siblings, aunts&uncles, cousins, my grandmother's brother, later on kids from the next generation. At first it was heavily used, but later there was demand for a Facebook group (which I also set up), and the mailing list has dwindled away.
I don't see any way to do without a Facebook account. But I don't put any content there. And I don't read my "feed", only a handful of individual groups I belong to.