There is another route. Have you ever been somewhat confrontational with someone? Ever been cut off and shout your head off? Ever told someone to stop smoking around kids? Yes? Well, then you might be able to go knock on the door and give them the, "You
will stop." statement. No threats, just posturing and a very serious look. Bring some other neighbors. If you appear united, you might just scare them into submission. If that doesn't work, I can come over.
I realize it's not the most mature and peaceful way to get things done, but consider it from their perspective. They view you as pesky, nosey neighbors who won't shut up. If you change their idea of you, make them take you seriously, you have a better chance of preventing problems like the lawn inncodent.