To keep them out of your account, you’ll need to change your account password… If you can’t do so, I recommend contacting Xbox Support through chat, phone, or Twitter to see what they suggest.
Select the account that you want to remove from the family group. Select Remove Name from a family where Name is the person’s name that you want to remove. Select Remove from family to confirm that you want to remove the family member.
Open the guide by pressing the Xbox button on the controller, then choose Profile & System Settings Account Family settings Manage family members. To confirm your choice, type in a password or passkey. Select the account you want to delete, then hit Remove from family.
If you’re concerned that your account may have been hacked, we recommend changing your password and securing the settings. On the Security page, where you may also remove all recognized devices as a trusted device, you can do so. For more information on account maintenance and protection, see Security basics
One victim discovered a security flaw on Xbox.com, according to which an attacker may exploit an unlimited number of password attempts to gain entry to any Gamertag they choose by learning the corresponding email address and launching the site with a password generator.
