How to only share iTunes and not allow purchases

Basically just want to share iTunes with the family sharing plan. And not have my card billed for other purchases.

We'd all like to have our cake and eat it, but it isn't possible. Other members can put store credit on their accounts which should be used first, but family sharing requires that the organizer underwrite all purchases that cannot be covered by store credit. You can manually copy files from one computer to another in your household.