Xbox game pass Ultimate not accessible

Also, if you purchase Game Pass first, then it would be converted to Ultimate and if you cancel ultimate, you would lose your Game Pass subscription. So if you do cancel Ultimate, do it first before you downgrade to just Game Pass.

Which subscription are you downgrading to, is it Xbox Game Pass, PC Game Pass, or Game Pass Core?

If Game Pass Core, you will only have access to just over 30 games that are part of the Game Pass catalogue, and online multiplayer.

If Xbox Game Pass, you will have access to all the Game Pass games on the Xbox Console, and no online multiplayer.

If PC Game Pass, then you will have access to all the Game Pass games on the PC including EA Play, and online multiplayer.

You need to have a Xbox Game Pass or Xbox Game Pass Ultimate subscription to access Game Pass games any you want to play.

They will not have the Xbox Game Pass Ultimate subscription on their account but they'll be able to have access to the game pass library and play online games due to you having the Xbox game pass ultimate.

What is the exact issue that they're experiencing?

Just to clarify there are 3 services on Xbox...

Xbox Live Gold: give you access to online multiplayer, Games With Gold, discounts and other promos.

Xbox Game Pass (console): Give you access to a catalog of 100+ games that you can play and discounts for those games.

The third one is:

Xbox Game Pass Ultimate: that give you all the benefits of Xbox Live Gold and Xbox Game Pass (console) plus give you access to Xbox Game Pass (Pc)

So, the best option is Xbox Game Pass Ultimate!

Regards!

You can add the 24 months of Ultimate to your existing subscription as long as it won't go over 36 months. If it were to go over the 36 months, you would need to wait until you have 12 months or less remaining on your subscription before redeeming the 24
months of Ultimate.

https://www.xbox.com/en-US/xbox-all-access#faq

An Xbox All Access purchase includes 24 months of Xbox Game Pass Ultimate. So, what happens if I have an existing Xbox Game Pass and/or Xbox Live Gold membership when I purchase a console with Xbox All Access?

If you're already an Xbox Live Gold or Xbox Game Pass member, any days remaining in your membership(s) will be converted to Xbox Game Pass Ultimate at a conversion ratio when you redeem the 24-month Xbox Game Pass Ultimate membership and added to your Xbox
Game Pass Ultimate membership up to a maximum of 36 months. Xbox Game Pass Ultimate memberships are limited to 36 months.

If you’re already an Xbox Game Pass Ultimate member, wait until your existing membership has a prepaid balance that is less than 12 months before redeeming the 24-month Ultimate membership through Xbox All Access. You will be unable to redeem with more than
12 prepaid months of Xbox Game Pass Ultimate.