So I've had my XMPP server for awhile. I did end up getting one of my daughters to use it, but her sister does not. I'm assuming its because she has an iPhone, and the XMPP clients sort of suck for it.
Going to try another approach on getting them to use something other than FB Messenger. This time with Matrix. I have the server set up on my Cubieboard 2, just have to sort the NGINX reverse proxy. With only a few people using it, I don't think it will eat too much RAM.