Monero, Graphene and Tor.
Discussion
Please don't endorse graphene (suspicious sponsoring and compromised hardware) nor TOR (confirmed government monitoring and funding).
Instead:
Monero, PostmarketOS and I2P
I absolutely love i2p and I am suspicious about Graphene being based on Pixels (for now). That said your family is running fully compromised mobile phones endangering not only themselves but the conversations you have with them. For them it's a gigantic leap forward to use Graphene over anything else.
Afaik Postmarket is not a hardened Linux, so different attack vectors may apply.
We need an open hardware phone which is not possible at this point in time for regulations. You could have a secondary device without baseband.
Using Googleâ„¢ hardware is an immediate loss of privacy and puts you up a few notches for agencies to pay more attention to what to do.
Between using a no-name hardware from China or something from Google, the first option will always be better because both devices are from China anyways.
You might as well just be spied from eastern agencies rather than adding western agencies too.