i would go to the local bikie gang or similiar, give them a grand in cash to come around and beat the shit out of the low lifes next door and drag them out kicking and screaming and leave in the street..
nothing straceable back to you..
I would not put up with this shit you are coping..
had a mate in cairns that got new neighbours in and they were drug dealers and general scum and were doing the some as what you are coping
he went and saw the local gang ( no names) paid a fee in cash and crownies
within a few days the problem was fixed....
seriously the cops are useless in these situations,if you want something done sometimes you have to do it yourself
dont sell because of them..