Your Family Sharing group is set up with the organiser paying for purchases. You can turn this off and require each member to pay for their own purchases.
However, if this setting is chosen the purchased content cannot be shared.
See How to share purchases with your family which says
If you're the family organizer and you don't want to share a payment method with your family, turn off purchase sharing. When purchase sharing is turned off, you can continue to share subscriptions like Apple TV+ and Apple Arcade. When Purchase Sharing is turned off, everyone must use their own payment method.
See your Purchase Sharing settings in Settings on your iPhone or iPad or in System Preferences on your Mac.
Turn off purchase sharing:
- On your iPhone, iPad, or iPod touch, tap Stop Purchase Sharing.
- On your Mac, click Turn Off, then click Stop Purchase Sharing