Apple Music Family Plan

As long as somebody had continuous coverage during transitions in plans they will not lose content. o in your case, your taking on a Family level plan will cover everybody else in the family group. There will be no break in coverage. Just make sure you have things set to share the subscription.

Add a family member to your shared subscriptions - Apple Support

Hey there Wiggum44,

While we recommend reviewing the entire article above your post, it explains that each of your Family Sharing members would have their own Apple Music library separate from each other. Here's the link again just in case you needed it: Get an Apple Music family subscription

As you have a Family Sharing group set up, and if you get the Apple Music family subscription, it'll be shared among your family members.

Cheers!