After a bit of research, I landed on Mattermost. I explained the reason for the shift, and migrated the whole family over sometime in 2019. As far as the family is concerned, the process was painless, and other than the lack of collapsible threads (recently fixed as mentioned in TIFA!) everything has been great. I run the whole thing on a $5/mo VULTR VM, that also also acts as a WireGuard and PiHole server.
On the backend, I’ve only had one major bump [0]- I went too long between server upgrades (I think I jumped from 5.21 to 5.29). The SQL encoding changed and caused messages to stay “unread.” Took me a day to find/correct the issue, and it’s been smooth sailing ever since.
[0] https://forum.mattermost.org/t/solved-after-upgrading-to-5-2...