If you want to invite someone to join your family subscription, read below:
The way Spotify Family works is that each person creates their own Spotify account first if they do not already have one. For everyone to create a Spotify account they will need their own email address.
Once everyone has their own Spotify account you then invite them to join your family plan and then they sign in with that account in the app. Then everyone will be able to listen without interrupting the other users.
Check out these pages for help with the Family Plan: