Is it possible to have 2 step verification with multiple account users that have different cell phones and not just the account holder?
No, you can’t as of now. Hopefully they will allow an authentication app to be used as well in the future.
On our devices, Shared Users receive 2SV [code sent to email] or 2FA [code sent via SMS(Text Message)] on the device they are using to log in to the ring app.