Lol, welcome to the club!

God how I despise SMS, and I can’t get anyone off it, even if other options are easier to use than SMS, much more robust, faster, more flexible, etc.

There are a couple messaging apps that are self-hostable (like I believe SimpleX is). Litewire is one. At some point I plan on hosting one myself, and preconfigure accounts for friends/family to make it even easier for them. Maybe that will get them on board.