Oh Sierra, to hear about this dog's life (and that of the SBT for that matter) has me almost in tears.
Easy one for me cause I love the breed so much, so no way could I do nothing like the rest of your neighbours.
My first port of call would be the local council. but I guess that's easy for me to say as I know the dog control unit at my local council. By law (to my understanding) a council and the DPI DO have laws pertaining to dog ownership, and care must be given to them. I would certainly be discussing this istuation with them at length!!! If this situation is that bad, no control unit worth it's own salt could fail to see the lack of care given by these owners.
Failing the local council unit, approach the RSPCA I guess. I've never needed to do that, so have no idea quite how helpful they would be, or not.
But with the local council, it's a catch 22 I'm afraid. The dogs are aggressive. That issue could work in your favour if you keep a close eye on the situation.
Aw, I feel sick... Some human's are sick mongerls, they really are!