I used to be a big proponent of Signal.
It was incredibly easy to have friends and family download the app and replace their SMS app with it.
Almost zero change or learning curve on their end, and we all got increased security when we used it.
Telling your parents to download yet another new app to talk to just you is a no-go and sabotaged their goal of increasing security for people at large.
as you didn’t mention Calyx, are there any security/privacy benefits of using it?