Multiple Gold memberships necessary for family on multiple Xbox Ones?

if he is only going to be playing on his Xbox One you can set the new Xbox up as your Home Xbox and that will allow him to share your Live Gold subscription as well as all the digital games purchased on your account.

this link explains everything about setting it up

https://support.xbox.com/en-GB/games/game-setup/my-home-xbox

you can set your account to automatically sign in on your Xbox then set a Pass Key for purchases, then anyone who signs in on your Xbox (with their own account) will still have access to your Gold and games

hope this helps

edit: I forgot to add a link to setting the Passkey for purchases

https://support.xbox.com/en-US/my-account/security/passkey-purchases

The games were all purchased with my account/Gold membership... And I guess if I set his Xbox as "home", games purchased for me and the rest of the family won't be accessible for the new Xbox...? Only on his?

Of course, I could just let him keep my account and access to Gold on his Xbox, but then I reckon I'd run into trouble if we were to try and log in at the same time?

Just so I understand you correctly:

You have your own account with Games and the Gold membership.

And "he" is the kid that gets the "old" Xbox One, while you put the new Xbox One X in the living room for the whole family?

In this case:

Either wait until your Gold membership runs out, or cancel it immediately on your account (getting a refund for the remaining full months), and buy the Gold membership for the account that is NOT usually playing on the Family console.

Then the Gold owning account can play on any console in the world (or just your household), as the Gold membership is tied to the account.

Then have the Gold owner share Gold to the Xbox One X in the living room for the whole family.

However, for the games, you can't move them as easily.

Since you own the games, you can only share them to one console (your account's Home Console).

In the future, you should consider having your kid buy the game. Similar to the Gold membership, digital games an account buys are tied to the account. So the account can play them anywhere, as long as that account is connected online.

Additionally, that account can designate one console as the Home Console, which will then share the games to anyone playing on that console.

So set the living-room console as the Home Console, as most of the family seems to play there.

If there are a lot of games your kid wants to play on his own console, you might have to have your own account signed in with a second controller, or buy the games a second time for that kid on the "non-Home" console of your account.

Also keep in mind: Do NOT change Home Console's unnecessarily. Each account can change it's home console only five times during 365 days.

Thanks for your quick reply, btw.

Thanks for your reply. I'll look into it when the new Xbox is purchased.