I want to use my own credit card instead of the family plans credit card but it won’t let me delete his card and add minw

The payment method for Family Sharing is automatic:

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 it cannot bill the primary payment method, the Organizer will need to make another payment method the primary method.

- "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/HT201079

- How App Store and iTunes Store purchases are billed - https://support.apple.com/HT201359

- Check your Apple ID balance - https://support.apple.com/HT202359

- Change, add, or remove Apple ID payment methods - https://support.apple.com/HT201266

If you are not the organizer, you cannot use your own credit card. If you are the organizer and wish to change the payment method:

This document explains how to 'Change, add, [review,] or remove Apple ID payment methods' on a Mac or Apple mobile devices; click here --> https://support.apple.com/HT201266

Change your Apple ID payment method if you don't have an Apple device --> https://support.apple.com/HT210755 - PC, MS Surface, Android, Chromebook, online at tv.apple.com

'If you can't remove your last payment method or use no payment method with your Apple ID' click here --> https://support.apple.com/HT203905

- If you are updating an old card and have ongoing subscriptions, or are the organizer of a Family Sharing group, you may need to first add the new card and make it the primary payment method before deleting the old card.