You are all sharing the same Apple ID. It is recommended that each person have their own Apple ID. You can share purchase from iTunes, the App Store and iBooks by using Family Sharing.
Family Sharing - Apple Support
How to go about setting it up.
Set up Family Sharing - Apple Support
It is possible to share an Apple ID to share purchases, but things can get murky. If you all share the same iCloud account using that Apple ID, you will really have problems sorting it all out.