Two accounts? How?

you can try delete the account from you're sister Xbox and try log in again https://support.xbox.com/en-US/games/game-setup/my-home-xbox

forums.xbox.com/.../12.aspx

please read here

only one gamertag per windows live id

however you will have to create a third windows live id an d then login into the account that has the windows live id you want

change it to the third dummy windows live id

then the one you want windows live id is free then goto the gamertag you want to change

then change it to the windows live id you want

As previously posted merging the two accounts is not possible.

The reason you are getting this message is that Hotmail/Outlook accounts are already MS accounts and can not be added to a second account as an email address used to sign in because the system will not know what account to sign into.

What you can do is this though I just tested it with my own.

Once you pull up the xbox app on your PC in the upper right hand corner you will see the X and minimum and maximum buttons with a circle next to that, that may show your avatar in it if you click on that circle at the bottom of that menu there is a choice
to sign out this will allow you to sign out of the current profile that is signed in once signed out and you click on that circle again it will give you a choice to sign in it will sign you back into the account currently signed in on your PC but it will also
give you a choice to choose a different account to sign into (this is just for the xbox beta app) this will allow you to sign into that app with your @live account.

This would be the only way that I can see that you would be able to use your @live account on your PC for your game pass.

Thank you for the reply, this is an idea I will try, although the only issue would be that in signing out from the xbox app also signs me out from other related MS apps across my system. So figuring out a way to isolate the account being used on the xbox
app from the rest of my PC may be a future solution to this.

As previously posted merging the two accounts is not possible.

The reason you are getting this message is that Hotmail/Outlook accounts are already MS accounts and can not be added to a second account as an email address used to sign in because the system will not know what account to sign into.

What you can do is this though I just tested it with my own.

Once you pull up the xbox app on your PC in the upper right hand corner you will see the X and minimum and maximum buttons with a circle next to that, that may show your avatar in it if you click on that circle at the bottom of that menu there is a choice
to sign out this will allow you to sign out of the current profile that is signed in once signed out and you click on that circle again it will give you a choice to sign in it will sign you back into the account currently signed in on your PC but it will also
give you a choice to choose a different account to sign into (this is just for the xbox beta app) this will allow you to sign into that app with your @live account.

This would be the only way that I can see that you would be able to use your @live account on your PC for your game pass.

You can't "merge" accounts, however I think what you may be looking for is changing the associated email for your Xbox Live account?

If so, here is a link that may be helpful to you. https://support.xbox.com/en-US/my-account/microsoft-account/change-email-sign-in-for-microsoft-account

If this has not solved your problem, please let us know so we may further assist you.