When I see things like this, I think you need to be extra concerned. It's the people who say we are great friends who would never have an issue who tend to be at greatest risk when conflict comes up.
The fact is, you're going to be crammed together with 3 other people in a car - sleeping together in a tent - for a month, and from the sounds of it, you only plan to have one person driving. If there is one thing I can guarantee is that, at some point during your trip, you will have conflict. It is much better to prepared for it now, and lay out how you will deal with it, than have problems on the trip that fester because you didn't have a plan.