That’s definitely another way to get the phone’s “voice” across! Glad it worked out for you. No more lost phones!
While that’s fine, that’s not exactly the intended use so that’s why you are running into problems as you can’t force volume to go up from another phone.
Start putting on DnD instead of lowering your ring volume to zero, and you can make it work.
If you don’t want to deviate from your out of the ordinary use case, then your best bet is some parental control app that allows you to view each other’s location.
Settings > Sounds & Vibration > Do Not Disturb > Select “Favorites” in the drop down under Exceptions.
Then in your contacts app, favorite each other and test it out!
Can you not whitelist each other as a contact that will override the mute?
I should have been a bit more clear, I meant putting your phone on silent and still wanting to be able to call each other / ping each other to make a noise.
THAT use case is pretty rare.