I use XMPP with "regular folks". At least on Android it works well to point someone to https://play.google.com/store/apps/details?id=im.quicksy.cli... and that's it.
first it automatically trust the devices but if you want you can improve it with manual verification :
"TLDR: Automatically trust all new devices of contacts that haven’t been verified before, and prompt for manual confirmation each time a verified contact adds a new device."