They did not appear to be armed, so there's that. But even if they had been armed, shooting unidentified people would probably result in the shooter being arrested.

Without knowing more about these people it's not easy to say what course of action would be appropriate. Certainly contacting law enforcement at the very least.

But these 4 guys could have been anyone. Border Patrol scouts, hunters, American patriots, invaders... who knows, especially from the scant evidence of this short video.