I can answer this partially. And issue a complaint. As we know family members are slaved to the payment method on the master account (that's me). I often buy iTunes cards discounted and keep a balance in my iTunes account. I bought two $100 cards discounted by 25% on Black Friday. However, when family members buy anything, instead of being paid from my iTunes balance, the payment is made from my credit card on file. This, is stupid, Apple. Fix this.