People form study groups all the time, it's a great way to learn. Since it's a free online course all of the benefit is what you actually learn, there is no way to cheat. At least that's my point of view (I am not in any of the classes, but wouldn't hesitate to co-work on stuff if I was).
Again, maybe it's just me, but this is a free online course that everyone is doing for their own knowledge. There's no degree being granted and it doesn't count for anything. I wouldn't bother to read the rules and certainly not attempt to follow them. I would try and learn the material as best I could, however that is.