Ah, I disagree that kicking the horse behind him/her is a problem. If another horse is going to run up into my horses butt gettin in his business, he will get what's coming to him. :P If anyone so much as touched my horse, trained or untrained, without my explicit consent, I would be coming after them with pitchforks, hoof pics, and anything else sharp. Props to you for being calm and cool about this, and seeking advice, If it were me, these people would bleeding and I would be in a straight jacket.
There are a lot of red flags with this place OP. I suggest finding a better boarding barn. There are barns out there that are run by sane, reliable people, not nut jobs. You are not in one of them at this time.