Hello and welcome to Apple Support Communities geekymom63,
We see that you have a question about changing from individual Apple Music plans to a family plan. We'd be happy to provide you with some information to help.
To answer your question, yes they will still have access to their music. You can also set up Family Sharing if there is purchased music from iTunes that you might want to share with the family as well. You can also share apps, games, and lots of other purchased content with Family Sharing. The articles below provide some more details, if needed.
Change your subscription plan
Get an Apple Music family subscription
Set up Family Sharing
Thank you for using Apple Support Communities.