If going to the cops to get this stopped is not an option, and I am not saying that it isn't, then perhaps it is a subject that should be taken to the people in the neighborhood. I would see what they have to say about it, anyway. I have heard of all kinds of solutions to these problems here and many of them work very well, depending on the circumstances and the people involved.
Three stories of people taking things into their own hands that I have heard here:
1. A heavy guy in a colonia knew who the people were that were robbing and beating people, and he had someone do a drive-by hit on the guy who was the alleged instigator.
2. A guy who was having problems had a cop for a friend. The cop came over one night and busted a cap over the guy's head as he was about to do some kind of vandalism.
3. A "sting" was set up with big guys in the wings and the people were caught, after a big fight.
If the neighborhood is involved, they may also be able to put pressure on the people if they are malleable in some way.