Hoping someone on reddit can help!

I live in a duplex house in Western Australia and my neighbour in the other half of the house has welcomed 10-15 people to live in the tiny 2x1 house. He’s enclosed the patio and built a little granny flat in his backyard.

There are numerous cars outside and the noises from the house are causing a disturbance.

Are there any rules in WA governing maximum number of occupants in a house which is NOT rented?