Is that possible to edit the Questings online (inside of the Multiplayer Server? )

Yes. You can also have multiple editors at the same time (just try to refrain from editing the same quest at the same time)

Thank you, i will do that :D

Is there a way to disable the rewards on the NEI?

up :D

no it can't be disabled. Can you not keep reopening this thread. These questions are better suited for the forums where other people can help you just as well.