Before the fourth checkpoint, Qin Wushuang and his group were indeed stopped. There were only five disciples guarding this checkpoint along with an Elder overseeing the situation, in total there were only six people.
In terms of absolute power, these six people were certainly inferior to Qin Wushuang's group. However, since this checkpoint was an unavoidable path to enter the Nine Refined Mysterious Wind Valley, it was set up with extremely powerful mechanisms and spiritual formations.
As soon as foreign enemies invaded, they could initiate the mechanism and the formation. The power of the mechanism and the spiritual formation far surpassed the power of the people overseeing the place.
Therefore, despite their lesser numbers, Qin Wushuang and his friends would not dare to charge recklessly in. Unless they could kill all six guardians before they had a chance to trigger the formation and the mechanism!