Why can a member of the family plan control music from a separate location?

[#1]

When listening to Spotify in my car, if my husband is listening in his car he can change or control my playlist.

[Eni]

Hey there, 

Thanks for reaching out about this here in the Community. 

Based on what you mentioned it sounds like you're logged in to the same account. In this case, we suggest that you sign out everywhere by following the steps here.

If the issue persists, can you let us know how you're connected to the car?

We'll be on the lookout.