1. Try not to be alone - either you or your wife. Better to have someone with you for a witness.
2. As soon as an attack starts, pull out the cell phone and clearly state with the recording started "I am recording this."
3. Don't escalate anything. Stay calm, and be as nice as possible, keep your voice tone very low and quiet. The more civil you are, the more it builds your case.
4. Write down past events as accurately as possible, when, where, what was said as best you can remember. Keep it factual, not how you feel.
5. Go down the chain of command. First start with telling this person you are offended and do not wish to continue this method of "communication" and that you will notify authorities. All said quietly and firmly.
6. Proceed to the owner/manager of the site. Always start there so they are aware. They should tell you how they are going to handle it and when. They should also tell you what to do if it happens again and who to report it to. Emphasize that if it continues you will report it to authorities.
7. If nothing happens and this persists, then go to the local police. Take all of your documentation and who all you have reported this to and when. That will give them a lot more information to go on and proceed with a plan rather than to "wait and see if this happens again" kind of thing.
8. Be prepared to move. The owners/manager could ask both of you to leave. I think he would be within his rights to do so but I would also think they would likely give your money back.
9. The hardest thing to do in these cases is not react. I have found a smile and reassurance can help but if the person is truly mentally ill, all bets go out the window.
Best of luck with this and let us know how it turns out.
EDIT: I might add that I was a teacher/administrator for 36 years, I have seen one or two of these. Yes, parents can be told to not enter the school because of their behavior.