Xbox PC app shows duplicate copies of games in "Games I own" section

as Jrocker mentioned above any game you owned digitally back on the 360 will transfer over into your games and apps section on the xbox one in the READY TO INSTALL SECTION

and with hard copies of games you'll need to install like any xbox one game.

As far as I know it's still available, I have looked on the game pass app and it's still shows under the pc section as well as the xbox section and is there for downloading

Apologies if it wasn't clear in my post somehow, but they are not in the ready to install section of the game itself, or the games and apps menu. They don't even show as free in the xbox store, only on the microsoft website, despite me owning them. I've
even tried pushing the download from the xbox app on my laptop (where they show as owned), as soon as I do my xbox says “you need to install the game or app for this”

You should be able to find the game in my games and apps. If it's not showing try looking in the owned games section in Full Library, which is also in my games and apps.

Is your xbox still his home xbox?

Are you seeing the game in the ready to install section and trying to install it?

Once you make your xbox his home console any digital game he owns should automatically show up in the ready to install section of your console.

Have you tried playing any of his other games and if so do you get a message that says are you sure you own this game or app if so sign in with the account that owns this game or app.