The payment system is a bit more nuanced that an earlier post would lead you to believe.
Based on: https://support.apple.com/108774 and https://support.apple.com/HT201359
1. If anybody in the family buys or subscribes to something, Apple first attempts to charge the item to that individual's Apple Account (Apple ID) balance, if any.
2. If a family member does not have enough personal Apple Account balance, any excess will be charged to the Family Organizer's primary payment method (usually a card of some kind). The Organizer's personal balance will not be used for purchases made by other family members. If Apple cannot bill the primary payment method, the Organizer will need to make another payment method the primary method. With Family Sharing the Organizer always has to have at least one functioning payment method.
Also note: "Some purchases, including gifts, can't be billed to Apple ID balance and will be charged to the family organizer's payment method." "Some subscriptions might not be charged to Apple ID balance."
Ref:
- Family purchases and payments - https://support.apple.com/108774
- How apps, content, and subscriptions from Apple are billed - https://support.apple.com/HT201359
- Check your Apple ID balance - https://support.apple.com/HT202359
- Add a payment method to your Apple ID - https://support.apple.com/HT201266
Adding funds to your Apple ID balance:
- https://support.apple.com/HT201209
- https://support.apple.com/HT208687
From: https://support.apple.com/HT212253
"If you're the family organizer and you don't want to pay for family members' purchases and subscriptions, you can turn off Purchase Sharing [ https://support.apple.com/108774 ]. When Purchase Sharing is turned off, everyone must use their own payment method. When Purchase Sharing is turned off, family members can share subscriptions, but they can't share individual purchases like apps or books." <-- I presume that means movies also cannot be shared unless they are part of an AppleTV program.