Ask everyone to sign up for different methods of communication
That's exactly what you are doing by insisting on Facebook use unnecessarily, when email is the true common denominator (doesn't everyone in your friends list have email?).
Re:Facebook – You are the Product
by compiler-guy on Thursday August 17, 2017 @08:07AM
(#15035941)
Nearly everyone is already there, and the number that isn't continues to fall every year. Yes everyone already has email, but list management and group organization is much worse. Even compared to Google groups.
And the fact is that most people prefer it.
Those are real tradeoffs that many groups aren't willing to accept, regardless of how willing a single person is to shoulder the burden.