Well, in a resonance structure only electrons (and therefore charges) move.
The negative nitrogen has 8 electrons fulfilling the octet rule but only 2 bonds and is therefore negatively charged.
It can then push one free electron pair onto the sp2 hybridized carbon and create a π-bond but due to carbon only being able to have four bonds the π-bond between the two carbons is removed and the electron pair shifts onto the "left" carbon as a free electron pair.
I think the third resonance structure doesn't work since the carbon directly bonded to the nitrogen would exceed the octet rule if it would get another free electron pair from nitrogen, so only the first to should be valid if I'm correct?