Quick Question About Multiplayer Mode For PC

Hello,

I have a question about playing multiplayer mode at pc like i said. I would like to buy deluxe edition, but i wonder if i can play with my bro. I have 2 Pc's in my home and we would like to play together. Purchasing 1 game will be enough? or should we buy 2 games? 

P.S: We are using same network(Same modem, internet connection etc.)

Thanks for answers.