Setting Xbox One X/S and a Xbox Series X/S both as Home console simultaneously

Hello Rhmd, to do this, you need to set the Series S as the home Xbox, then make sure both your account with the games on the Series X, and his account are both signed in on the Series S. Once you do that he will have access to all of the games on the
Series X from his Series S.

i set the series X as the home xbox and it did not let me play MW3 even though i own it.

Edit : When i swapped the series X as my home console it took away MW3 on the series S too. So now i cant play on both consoles.

No such thing as an Xbox One Series X. The Xbox One family of consoles has an S and an X but are still just Xbox Ones. You need the Series family of consoles. The Xbox Series S or Xbox Series X. These are different from Xbox One S or Xbox One X.

The "One" and "Series" are the console types.

The Series S/X version is only playable on the Series S/X and will not work on the One. The Xbox One version will work on both.

The Xbox One S is a variant of the Xbox One console. Xbox Series X/S is the newer generation of consoles. Xbox Series X/S enhanced games are only for the newest consoles not the Xbox One S. You would need to purchase the Xbox One version of the games not the X/S version of them.