I've been using XMPP since about 5 years for family texting, file/video sharing, and video calling. It works great, and I would highly recommend it.

What works for us (all android) is Prosody + Conversations app (or Blabber is a free version). There are a few guides online for how to install & configure the prosody server. It's fairly non-technical.

Honestly, it works just as well as whatsapp - except there's actual privacy between users. Family messaging is a great use-case as everyone can be on the same server.

Conversations is free if you get it via fdroid. Don't let that stop you from donating for development though.

I've been doing the same thing for my family for the last four years and it's been working really well. We're all on Android and using Conversations as well.