ULPT Scary Neighbor

So I just learned that one of my neighbors who I barely know has an adult son around 18 or so and he has been walking up and down the road motioning to people like he is going to shoot them with his finger. This is very concerning to me because his father literally owns and operates an armory out of their home, I thought of maybe reaching out to the mom on facebook about it but I do not really know what woud be the most advantageous way to ensure that the parents are aware but not incur any kind of blow back from the family or the son. What would you do?