How do you play one computer two controllers?

I have one steam account. Bought the game to play with my wife.. I have wine Steam  on Ubuntu and Steam on my PC.  

I can't figure out how to play two controllers on the pc.  Is this possible? Please provide instruction steps.

Do I need friend pass?  Can you describe how this works when my wife has no and does not want a steam account (has older MacBook)? Is it necessary?  Can you describe steps with my hardware on how to use? 

Of course the expectation is that we play in the same room. Split screen on one screen.