My goal is to get to a safe area ASAP, as I really dislike having guns pointed at me. I am assuming that you have a mountain on one side of you, and a steep cliff on the other. If not, is it possible to exit your vehicle and take to the woods and once behind cover communicate with them?
Another option is to wave and act like nothing is wrong and manuver around the other vehicle, or back up to a pullout or wider shoulder area to allow them to pass. The fact that both occupants of the vehicle are armed is a great concern to me at this point given the expressed posturing you wrote about.
You do not know that these folks were up there stealing stuff, eventhough that is the most likely explaination as to why they were up there, and theft is not usually punishable by death. The two have the ability, some implied intent based on their actions, and the means to cause your death, but I think most juries would have a hard time buying the intent at this point by what you typed.
They could argue that the rifle bearer got out of the truck due to your aggression, or some other such, and was only taking a more tactical position in the interest of safety and not because they had any evil intent towards you. It also could be a property owner checking on fences after he saw the lights from the real thieves as they were stealing stuff. It would sure suck to be you after you shot a rightful property owner that, after having seen the vehicle lights of the real criminals, went to investigate only to be shot by a company employee.
Sometimes the poker game of life deals you a crappy hand, and you have to play the cards you are dealt. Being that I am not there I cannot tell you exactly what I would do, as I cannot read their mannerisms and have no knowledge of the local culture. I can tell you that I would have to consider some options, none of which are favorable, and all carry risk.