Xbox Hub won't let me log in to another account because my cousin logged in to his!

Hello,

I recently was invited to the new Sea Of Thieves beta game so I downloaded the Insider Hub App and my cousin logged into his account (I wasn't aware he logged in because I was out) and he's under the age of 18: Screenshot
and now I can't seem to log in or sign out to his account because of this reason, and I have no idea what to do, I just want to log out and log in to my account so I can play the game, I've tried reinstalling but it just gave the same message.

Please help!

:)

 

Family account

There was only one gamerpic on the home screen and that one was mine. The xbox was off. He went to school. I turned on the xbox, it logged me in. He was not even in the house. The only pic by the log in was mine. The sceen was my color... there was nothing to indicate his account was logged in at all. Is there another way to tell. The player two controller was even off.....

One another note, how can you tell which controller is logged in under who?

 

Will we be able to play together?

Hi! My family and I enjoy the Gold subscription because we can all play each of the games, and compare scores, etc. We each have our own accounts on the Xbox.

But we're thinking of getting an extra Xbox so we can play the multiplayer games at the same time, with all of us logged in to our own account.

With my wife logged into her own account on her own Xbox, and me logged into the same game in my account on my Xbox, that would be so much fun! Will we be able to do that?