Manage family macOS logins
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 &quot;corporate&quot; 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 &quot;infrastructure&quot; 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 &quot;breach&quot; is contained and you don't compromise the rest.