Quote from Fractals 'R Us:
Don't waste time reasoning with unreasonable people. Don't waste time on some cooperative venture involving the neighbors. If they haven't dealt with it up to this point they are not going to. Go on the offensive and don't quit until those assholes are not a problem for you. My dad, he knew people, if he felt it was warranted, a couple of guys would come unannounced, beat somebody to a pulp and go their merry way. That way is inexpensive compared to long drawn out lawsuits but most people don't do that. I would start calling the police and suing the neighbors and never stop. Life is too short to have somebody ruin it for you on a daily basis. You can have fantastic surveillance nowadays. I have a Nexus7 tablet and an app that turns it into a motion detecting high resolution surveillance camera, it's just fantastic for that. If the guy is standing behind your car in the middle of the night, run into him... I mean it's a war on your sanity and happiness, get a game on... Start collecting evidence and don't ever stop because when those lunatics get to court they are going to be some of the best liars you've ever encountered. Go after them on the criminal level and the civil level.
I had a neighbor like that, I made it my hobby to defeat him at EVERY turn.. I learned a lot in the process...