remove person listed as mainpayment person administrator
Remove person listed as administrator for family sharing
Remove person listed as administrator for family sharing
See this support document, and follow the instructions for disbanding the Family Sharing group. Leave Family Sharing - Apple Support
If you are just concerned about the payment, the family organizer is the one responsible for all payments for Family Sharing. If you wish to change it, you will have to disband the group and start over.
remove person listed as mainpayment person administrator