You don't have to set up anything but the Family Sharing group to share your purchases from the iTunes & App Stores, including music, apps, books, etc. In addition to that basic Family Sharing feature, you can also add the Apple Music Family plan and iCloud Storage Family Sharing if you wish, but neither of those additional features are required to share your purchases:
Apple - iCloud - Family Sharing
Set up Family Sharing - Apple Support
Family Sharing - Troubleshooting
The articles above provide you with the instructions and the info about sharing purchases via Family Sharing as well as a troubleshooting article that may help if you have issues when you set it up.
The two article below explain the other two optional features that you can add if you wish:
Family Sharing with iCloud - Apple Support
Apple Music and Family Sharing - Apple Support