4) Can SM on overwatch react with Command Points to target genesteller move?
I am not sure about this. Here is what I think... Yes, a space marine on overwatch could take an action, however it would lose overwatch, and would not get to take the overwatch shot.
I think NO, because SM must shoot if he on overwatch. But i think that player can move another SM model, is it right?
Yes, if one space marine sees a genestealer action, a different SM may act.
5) is unjamming the gun cancel sustained fire bonus?