Manage family macOS logins

Solution 1:

Unfortunately, you've discovered the perils of having a single password for multiple devices/accounts. This would be no different than if it were an IT Manager who used the same firmware PIN and admin credentials across all school computers (I say that, because I inherited that exact problem).

Apple ID doesn't haven anything to manage this and "corporate" style solutions like network authentication or mobile device management is simply overkill for what you need to do. So, the solution is to use a different password for the admin account for each Mac and store them in a good password manager.

I use KeepassXC for this purpose. My personal stuff (like bank accounts and website logins) is stored on a different service, but passwords for my "infrastructure" is stored here. All my routers, switches, servers, etc. are stored in KeePass. KeePass is secure. If you lose the master password, you're not getting into to it - ask me how I know.

By having a tool to manage your passwords and using different credentials for each device, any "breach" is contained and you don't compromise the rest.