I don't know what you mean by "linked". There is no such thing with Apple IDs. There is Family Sharing but that only has to do with sharing of purchased and other material, nothing to do with account security.
What exactly is the problem now?
Click on this link to read what to do "If you forgot your Apple ID password" --> https://support.apple.com/HT201487
or go directly to this link --> http://iforgot.apple.com/
If you didn't receive your verification or reset email click here --> https://support.apple.com/HT201455
If you are being sent a verification code to a phone number to which you no longer have access, click on the next link to see the various ways of getting a verification code:
Get a verification code and sign in with two-factor authentication --> https://support.apple.com/HT204974
If you still need help:
Contact Apple for help with Apple ID account security "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues." --> https://support.apple.com/HT204169
Also read about "What to do after [or before] you change your Apple ID email address or password" --> https://support.apple.com/HT204071