Keep in mind, any Family Sharing actions you want to do to leave or disband the group will most likely require the Organizer. The organizer cannot leave a Family Sharing group. If you want to change the organizer, you must disband the group, and have another adult create a new one, which must be done by the Organizer.
Learn more ⇢ Leave Family Sharing - Apple Support
If you don't have access to the account, you might be able to try Account Recovery. Account Recovery is a process to get you back into your Apple ID account, if you use two-factor authentication and can’t sign in or reset your password, you can regain access after an account recovery waiting period.
Learn more ⇢ How to use account recovery when you can’t reset your Apple ID password - Apple Support
-Zachyy ✌️