manage family device

With the exception of a computer there is no such thing as a family device. iPhones and iPads are designed to be used by a single person unless you are doing a major ownership transfer. Parental controls can be used to manage a child's device:

See how to use Screen Time on an iPhone, iPad, or iPod touch by clicking here --> Use Screen Time on your iPhone, iPad, or iPod touch - Apple Support

With Content & Privacy Restrictions in Screen Time, you can block or limit specific apps and features --> Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

Are you asking about AppleCare? Read this support article to learn how to cancel your AppleCare plan --> Cancel or change the payment method for your AppleCare plan - Apple Support