Family Members able to erase my devices

I have the exact same issue. I don’t recall them having the ability to do this before.

Family members seem to have access to enabling “Lost Mode” and “Erase this Device.” —I say “seem to” because the option is there but I don’t want to test it entirely. On my son’s iPad, I clicked “Erase This Device” for my Apple Watch and it goes to the next screen and gives me the option to “Continue” along with the warning “All content and settings will be erased…”

This really is a big problem.

I'm sorry but what you are claiming is frankly impossible. They could only do that if you are all sharing an account (and are not using Family Sharing which is multiple accounts). The only other way would be if you used one of their devices to take control of a stolen or lost device and didn't sign out afterward.

Read these support articles to find out how to use the Find My app to locate a missing device or item. Click here --> Find your lost iPhone or iPad - Apple Support and Use Find My to locate your lost Apple device or AirTag - Apple Support

- A person can use the Find My app on a device owned by someone in their Family Sharing group.

Apparently it’s no longer impossible.