My son's phone rings when someone is calling me. How can I fix this?
Both answers above are correct. Just 2 different ways of correcting your problem.
1) both use different AppleID OR
2) Turn off the cellular phone calls through facetime when on the same wifi.
The new family system allows control over a minor's AppleID while still allowing them to have a separate ID and not able to buy anything without your approval.
You need to set up separate Apple IDs. One for each person.
Or go to Settings/Facetime on your iPhone and turn off "iPhone Cellular Calls"
I think must be the issue. Thanks. It only happens when we are both at home (using the same wi-fi).