Gottya. Yes I was thinking Mastodon. i guess Lemmy is by its nature public. I guess you would need to be able to address your posts to either public, users who are community members or become one, only current community members or potentially either of those two but excluding blocked users.

I feel like their are some common group communication design patterns that could be adopted that might make working through these options simpler - e.g public vs private groups, broadcast vs multicast communication, forward vs backward accessibility. But perhaps I just cant sleep and ita 330am...