Do you have animal control? I would think that maybe they could help you out. No hoof no horse right!? :) If you don't have animal control (i live in a small town and we don't) I would call the police dept and just explain what you saw and let them know that you don't want to cause problems with the neighbors but you noticed the problem. It could just be a case where the authorities can "help" the owners get the care the horses need and not take the horses from them. Good Luck I know this is hard, but your heart is in the right place!