How to switch Family Organizer
I’m unable to get family sharing on my phone
iPhone 14, iOS 17
To switch a Family Organizer, you must first disband the family group and then set it up again with you as the Organizer.
Leave Family Sharing - Apple Support
If a child in the group is under the age of 13, then they must remain in a group and can only be transferred to another plan. In this case, you should be able to disband all other members including yourself and set up yours. After that, the child under 13 can be transferred to you and the other organizer can then join your group.