Using unity on multiple computers with one account?

Hi, I have recently started a group with a couple of friends to build a game, but we're not sure how to all work on one project at once. Do we need a license to have one account for all of us to use? To work on one same project? Also, if we need a license, which one do we need? What is the maximum amount of people that can work with a certain license? Thank you very much!