For the time being, I would see about maybe creating a "safe area" for your chickens where they can not get to the property line...or moth balls. I know it seems like you are giving into their childish behavior, but I would not want to risk my chickens healthy and safety either! Continue to document...ect. Unfortunately I DO NOT think you are dealing with stable people here and THAT is really scary!!!!! Be careful and stay safe, but continue to make it clear to them that you are not putting up with this nonsense! They seriously need to get a hobby!!!!!