Two consoles, one account.

What you would need to do is create another account for the second user (or anyone else who wants to play). The first account you have can set one of the consoles as their Home
console in order to share any games or gold that have been purchased on that account. So the new account would want to use that console and the original account can sign in and use everything on the other console. Any progress made in the games won't be
able to be transferred over though. So whoever plays on the new account would have to start over.

basically what Metal Daz3 is trying to say is you cant be signed in to 2 xbox ones at the same time with the same account. you can have your profile on 2 different xbox ones but the cant be signed in at the same time once you sign into the second one the
first one will say sign you out and say you have been signed in elsewhere.

You can't use the same account in two xbox one consoles (be that just xbox one, s or x)

Yes. If everything is on your account, you would set his console as your Home so he can access your games and subscription on his account. Then you can use your console.

As long as you're signed in, your saves will be stored on the cloud. So they'll easily move between two consoles. You should see your game sync them when you start the game. It shouldn't screw anything up.