We have a family chat with 16 people in it.
the majority of people contribute according to their lives (ie - shift workers etc). We post the usual things like photos, check ins, arrangements etc. However my sister and her husband very rarely contribute. Even when you say Happy Birthday to one of their three children, they might respond or they might not. If someone arranges something, a picnic, a celebration etc - nothing. They then rarely come or if they do, they’ll just turn up or you have to ask them directly if they’re coming.
They rarely interact with any family events but do a lot with their friends. I have just presumed that they don’t want to and I respect that, but it leaves the rest of us feeling quite flat and rejected.