Family sharing multiple payment methods

See How apps, content, and subscriptions from Apple are billed - Apple Support, in particular this section.

Some purchases won't be charged to your Apple ID balance

• If you're in a Family Sharing group, purchases that you make will be charged to your personal Apple ID balance. If you don't have enough Apple ID balance to pay for the purchase, the remainder will be charged to the family organiser.
• You can't use your Apple ID balance to buy gifts or gift cards.
• Some subscriptions may not be charged to your Apple ID balance.

When you set up family sharing the family organizer undertakes to pay for anything that isn't covered by store credit.

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Each member can add store credit to their own account, which will generally be used for their own purchases ahead of the family organizer's payment method.

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yes you would just have to go on each device and put the info on to add a new method

That should work

Why tt2