Family Sharing - Understanding Content

We currently have multiple Apple devices (parents and kids). We are behind the times, and have continued to use one iTunes account on all devices.

I want to make sure I understand 'what' will happen to content if start using Family Sharing and then subsequently if we stop.

Today, my understanding/experience is that since we all share/use one iTunes id, all content is available on each device. Further, I believe I understand that content purchased under Family Sharing will default back to the organizer if/when a child leaves the Family Sharing.

|---- One iTunes id -------| ------- Family Sharing --------|--------- Child leaves Family Sharing

1. All content currently on a child's phone (from using one iTunes id) will remain on that device after changing the iTunes id and joining Family Sharing?

2. All content purchased by a child under Family Sharing will no longer be available once that child leaves Family Sharing?

As the organizer, I don't think I will want the content my child has purchased during Family Sharing. I simply agreed (or will agree) to pay for the content, but would want the content to go with them. e.g. A 17 year old child might want to purchase a lot of music I'm not interested in hearing. Under Family Sharing, I agree to pay for it, and other family members can listen to the music. In a several years, the child is on his/her own and leaves our Family Sharing plan. The music stays with me?