My cousin who I’m giving the gift card to HAS his own Apple ID. So if I’m reading it correctly he won’t be charged on his gift card if I made a purchase right
When in Family Sharing, a family member can use iTunes Gift card credit to pay for purchases.
“Family purchases and payments - Apple Support
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's card.
Make sure that what you were billed for is in fact the entirety of the purchase. If the purchase cost exceeds the itunes credit available in your child's account the remainder will be billed your account. Also the credit must have been redeemed onto the account, and be available before initiating the purchase. “
Source:
https://discussions.apple.com/thread/7898521