Apple id

I'm not sure I understand, but if you need to find another iD, see if you can recover the ID/password.

Apple ID - How to find your Apple https://support.apple.com/en-us/HT201354 An iCloud e-mail address is an Apple ID.

Apple ID - Find https://iforgot.apple.com/appleid#!&section=appleid

Enter the Apple (iCloud) ID and click Forgot Password.

Apple ID - Manage https://appleid.apple.com/#!&page=signin

Apple ID – Forgot Password https://support.apple.com/en-us/HT201487

If you are sharing the same Apple ID, you can't unless you do something like change the password, which would prevent them from using the Apple ID everywhere.