Hi there Keri,
We understand wanting to make sure you only pay for the services you use, and would like to help clear things up for you.
The first thing we wanted to point out is that everyone should have their own Apple ID signed into their own device.
Moving forward, you mentioned your son is paying for an individual Apple Music membership, along with you paying for one as well. If you're part of a Family Sharing group, and are the family organizer, we recommend that your son cancel his Apple Music subscription, and you sign up for a family membership. That way, you pay one fee for you and your family to share the same Apple Music subscription.
Another option to consider is one of the three Apple One subscription bundles. With the Family and Premier subscriptions, it'll include a family subscription for Apple Music. Here are more details: Bundle Apple subscriptions with Apple One
We hope this helps answer your question. Have a good one!