Family plan

Apple Music includes access to the full Apple Music catalog. Users can play any song or album available there (over 100 million songs available).

They can also download music for offline playback for a limited amount of time.

It also offers access to the iCloud Music Library which can match or upload any songs or albums on a computer to the cloud, and make them available to other devices signed in with the same Apple ID. (Do not share an Apple ID with anyone)

click here ➜ Use Sync Library with your Apple Music subscription - Apple Support

Each user, gets their own Music Library and it is not shared or mixed with anybody else's.

click here ➜ Apple Music - Apple

Do note, you do not own any of the Music on Apple Music. If the subscription is ever discontinued, any songs or albums added to your library or downloaded for offline music will be removed form your library and devices and stop playing.

Their library is their own, and continues to exist on their account. They don't bring it. It simply continues to be part of their Apple ID. The Apple Music subscription they have access to has no bearing on it.

You will not see that library yourself, but they should be able to continue using it normally as long as they don't cancel their subscription or have a gap between their previous subscription and having access to yours.

A Maximum of 5 family members plus the Family Organizer for a total of 6 people.

click here ➜ Set up Family Sharing - Apple Support