Simplex, element(or most matrix compatible messengers) session, bchat. If the goal is to get your family to switch over though good luck.
I don’t think I’m understanding this right cause it sounds like you’re trying to make it more fun by adding more rules. If there are 20 groups that are all about pickles that’s fine they each like running things their own way. Eventually one group gets popular and that’s where the majority goes. I think your frustration could better be solved with something like tags where groups could choose to associate certain tags words that makes search easier like tag: pickles-fermenting-homemade-cucumbers and that could clear up search from people just wanting to share pickle Rick memes.
Am I missing something I see a downvote button?
How difficult is it running your own instance. I’m very interested in that.