I've been increasingly successful in nudging my girlfriend to use Signal. She has a lot of old, close friends on the west coast and FB messenger has been the core of her communications with them.

Getting her to add it and see that a few people on her contact list were already on there, including her boss, and that you can audio/video chat was a big push. Still working on that, though.

Might be worth a shot:

https://signal.org/blog/signal-video-calls-beta/