Why can't my family access ultimate game pass?

But my subscription is for Game Pass Ultimate and not for Game Pass for PC... My family should have access to the games, right? Otherwise, what is the family plan for?

Hi there, my name is Gerardo and I'm an Xbox player like you.

Since Starfield is a game that only came out for new generation consoles (Xbox Series X |S) and you have an Xbox One, I imagine you mean playing it from Xbox Cloud Gaming. I is important that you know that when Game Pass Ultimate is shared through Home Xbox, only the account that originally purchased the subscription can use Xbox Cloud Gaming, as it is a feature that is not shared in that way. If any of the other accounts wish to play using Xbox Cloud Gaming it would be necessary to purchase the subscription separately with that account.

I hope this helps and I'm sorry for any inconvenience this may cause you.

If you have any further questions, don't hesitate to let me know.

On the Xbox One X only the account holder would get access to cloud gaming which you would use to play Starfield.

And that's why you can't access the game, you don't have currently a Game pass ultimate suscription active on that account

I upgraded to the Ultimate pass myself and the family still has access to my Gold and Game Pass games on the home console so you should still be good to go.