Q: What happens to iTunes credit when you use family sharing.

You can use the same credit card for sharing >  Apple - iOS 8 - Family Sharing

How to start an iOS 8 Family Sharing account to share apps, music, movies & more

the account with the store credit in it is the only one who gets to use it. Once it runs out, it will use the credit card associated with the Organizers account.

Thanks Sid, I was wondering this too. and presumably if a family member gets another iTunes card they can add that to their personal account and it will be used in the same way?

How did you find this out? Do you have members with iTunes credit in your family group?

Making purchases

After you set up your family, any time a family member initiates a new purchase it will be billed directly to your account unless that family member has gift or store credit. First, their store credit will be used to pay the partial or total bill. The remainder will bill to the family organizer. As the family organizer, any receipts generated by the transaction will be sent to you. Learn more about how iTunes Store purchases are billed.

Family purchases and payments