To expand with my personal experience, I self host a synapse server partly for the reason that i want my children (aged 8-14 now) to have a communication platform they can access to get ahold of me with out requireing a sim card. I do not federate, and i do not allow account sign ups. That keeps a pretty isolated instance while still allowing everyone on that homeserver to be able to talk to each other.

I help them get Element setup on each device. I dont think this is overly complicated, but i am sure i am a horrible judge of complexity… They have to enter the url of the server, then their password, then they need to scan a qr code/verify from an existing device. Or, they need to enter a second passcode to verify their identity. I help them keep those secrets in bitwarden, so imo, that complexity is an opportunity to explain some opsec and encryption!