Bought a second Xbox for my two kids and one user can only play on one console. How can I fix?

I purchased a second Xbox console for my two boys at our house. My first son is logged in and where our xbox live gold account is located. On the second new xbox we logged him in there as the “my home” user so games would transfer.

On the new xbox, they both can play games and all works fine. On the old xbox, only my first son can log in and play fortnite. When my second son tries to log in on the old xbox, it says he needs a live gold account. Very confusing since he is able to play
on the new device.

I have a family plan set up and we are on the same network, i don’t understand why my second son is limited in playing location? How can i fix? This seems so simple for Microsoft.

Thanks!

:)