Registering new Xbox one

When you're running through the initial setup of the new Xbox, it will ask you to sign into an account, so all you need to do is sign into your son's account. The account being on 2 Xboxes already makes no difference.

If you are going to sell the broken Xbox for spares/repairs, it would be a good idea to change the password on your son's account first, then if the new owner of the broken Xbox manages to repair it, they wouldn't be able to access your son's account as they wouldn't know the new password.

Rather than sharing an account, it might be better for your grandson to have his own account, then he can have his own achievements and game saves, and when he's old enough, his own friends list, online purchases etc. It is possible for your grandson to still access the digital games and subscriptions purchased with your son's account, so he wouldn't have to buy his own copies of games and own subscriptions etc. If you want some advice on how to set that up, I can help you with that.

yeah you need to register the new console first, assuming you have already registered your original xbox one and the Kinect itself..

Is this the site you're using to register your console? If it is, and you're not seeing the option there that you'd like to preform, I suggest giving phone support a call.

Yeah thats the site, I'll try entering it first then if I can't do what I want I'll call phone support. Thanks

I am getting the EXACT same error when trying to register through xbox.com on my computer. The old xbox is still registered and showing up on the account, but when I attempt to register the new one; I get the aforementioned error.