I have Game Pass Ultimate and a Xbox Series S and a PC. I want to play on PC while my Wife...

Yes, since you are a Game Pass for PC subscriber, you will also get EA Play included in that subscription. You will not need to purchase Ultimate. "This means Ultimate members can enjoy EA Play on Xbox
One, Xbox Series X and S, and Windows 10 PCs, and Xbox Game Pass for PC members get EA Play on Windows 10. "

Flight Simulator has not been released for the Xbox One. It's available for the Series S/X and PC. If you have Game Pass Ultimate, you can play it via the cloud on the One.

Forza Motorsport is not being released for the One. You would need a Series S/X or PC to play it or play it through the cloud if you have Game Pass Ultimate.

There Game Pass for console, which is for the Xbox One and Series S/X and then there's Game Pass for PC which is only for PC. They each have a lot of the same games, just console vs. PC, and PC Game Pass does have less games than console. If you would like to play games on both the console and PC, then you would want to look into Game Pass Ultimate which includes Game Pass for console, PC Game Pass, and Gold (which would need to play online multiplayer on the console anyway).

Sharing through Xbox is not done the same way a Nintendo Online subscription is done. You can't actually share the subscription, but you can set a console as your Home console and other people who use the console would then be able to access online multiplayer (if you have Gold/Ultimate) and any games you've downloaded from Game Pass or purchased.

To do this properly she needs to have her own account and loged in

Using the Xbox only and not cloud she can install nms

Only your account with xgpu can roam