Look I get that people love to shit on Signal because its not perfect, but this is the main reason I use it to call and message my family. It's a viable alternative to insane shit like Messenger and you should consider having your family members install it. It's incredibly easy to use.

Cue someone below me talking about how they set up a Matrix or XMPP server for grandma and its 'so easy' once you get the presence handshake working and if you're using a specific set of clients that support the right features.