Whatever you choose, the actual challenge will be convincing your family to use it just to speak to you.

Simplex

Element (X) and Schildichat (Next)

On Android, there is Quicksy, and yes, it uses phone number sign-up for ease, but it seems more private than corporate apps.

Without phone numbers, there's Conversations.im. There are some public XMPP servers with open registration, but you would need to find one, e.g. sure.im by Tigase lets you make aan account, but I don't remember if calls work.

Are you looking to self-host something as well? Snikket is all-in-one chat+calls, but you would need to host a server. (Still based on Conversations and XMPP)

Jami, Trifa or Nextcloud Talk.

@arsus5478 Conversations can do that. Requires an #XMPP account but you can create one through the app.