I confronted him about it and he has done much better, but continued fines would have cut into my cash flow in a major way.

I'd be very careful if you do decide to knock on the neighbor's door to confront them about the issue.

So, I'd very nicely ask in a way that is not confrontational, but lets them know that it might be more hassle than it's worth to deny you, because you may be looking into a disability discrimination complaint. 

You have to decide to either blow off the signing or confront him.

If the neighbors cross the line and do something physical / vandalize / confront , take swift legal action, but as an owner, just let them vent to you and calmly explain why you're not in the wrong.

And, she had other mail in there with her name on it - so we knew who had a rabbit snuck into her apartment.The problem was, we couldn't then confront her without letting her know the owner went through her garbage LOL. 

If confronted about this and their likelihood of liability, they may wish to settle. 

First year, the rise of his flaws, but protected to stay. 2nd year, the peak where you had enough and are willing to confront him about it where disputes happens, again but protected to stay.

You don't have to be rude or confrontational about it, you just need to be firm.

This may feel confrontational or uncomfortable for you to say, but if you need to do it.