Today's #FreeSoftwareAdvent is all about XMPP.
Snikket (https://snikket.org/) is an easy-to-install, and easy-to-administer, XMPP server. It is designed for families and other small groups. The apps for Android and iOS (based on Conversations, I think) are great.
Dino (https://dino.im/) is my desktop XMPP client of choice.
Profanity (https://profanity-im.github.io/) is a terminal / console XMPP client, which is incredibly convenient.
Why not have a fun festive project of setting up an XMPP-based chat server for you and your family and friends?