Adding account

A factory reset might help in my opinion. I am not sure but usually, a hard reset helps in many cases when there are account-related issues.

Also you can login to your Microsoft account from a browser and see all your devices, there you can remove yourself form all of them and then try again to login.

There is a perental control section were u can also set time time limits so your children can play for a hour a day and if they want to play longer or go on games above there age a email reguest gets sent to you and you can ever agree or not

I believe you can, juust go to account in the settings and select the sign in and passkey option, and set your key

You can prevent new account creation this way:

Go to the console settings, and under System should be the option to "Control offline content".

Uncheck the option to allow new profiles. You can also set other things like age restriction etc. Then create a passkey to protect these settings.

Yes you can! You can also add them as child accounts and use parental controls, add screen time limits, etc.