In fact, this is a big impossibility, not just a "little thing with no importance". The argument of "controlling the dream towards a second and a third level" would be acceptable if a one person dream. We are talking about seven people that share these different levels--too much of a distortion. The natural way to go would be each one of them walk their unique way since the second dream level. I can't accept this size of divergence.
Having said that, I close my eyes to that because I loved the movie. What I loved about the movie was the exploration of the mind features which I think to be accurate.
