Here are my non-legal thoughts: gather your evidence, get stat decs from friends who have heard the noise themselves, write a diary of noise events, record any noise that you can, and then go to NCAT for the imposition of fines.
Meanwhile, explain to your “not my problem” neighbours that if you take the OC to NCAT for failing to fulfil their duties, they will be in legal trouble anyway. And if the OC loses, they will all have to pay their share of the OC’s legal costs and you won’t, and they might have to pay your costs too.
That might sharpen their thinking into offering you some support.