Can two people play at once?

Using the game pass and 2 different accounts yes it should work.

so its using the game pass, we didnt actually buy state of decay, would it still work?

Hi there,

as far as I know you can't use the same account at the same time on PC and console and play a game.

What could work is if the account that bought the game played on the PC and you use your own account on your Dad's console (when your Dad has set his console as Home console)

See this link for some more information about the Home console setting:
https://support.xbox.com/en-us/games/game-setup/my-home-xbox

and also check, what is Not allowed to do when sharing games:
https://enforcement.xbox.com/en-us/home/staysafe#topic4

You wont be able to use the same account on 2 different devices at the same time.

It should, subscriptions are shared by all accounts logged into the home xbox. There used to be a bug where you'd have to install the game using the account that has game pass first before other accounts could play the game but I think that's fixed now.