how can i save these cats?

hi all im stuck in a predicament as a family i know is known to constantly breed cats in poor conditions and just keep letting them die and be replaced by newer generations. they dont even breed to sell, they just dont care about these cats and leave them to die in their backyard. weve asked them plenty of times to desex them but they refuse. theyre outdoor cats that constantly get raped and have offspring, only to end up dying from the constant birthing or they pass away from the fleas and infections they contract.

i feel immense guilt and heartache everytime i go to their house. i feel like i can do something but i dont know what. ive thought about adopting a kitten or two but i currently live in a 1 bedroom house and already own a cat. its not going to work out for me. ive thought about taking them all to a shelter but i dont know where to start. i know RSPCA can turn me away and say their space is full. theres also the problem of these cats not being mine so im not sure if i can just take them.

ive thought about reporting this family but im not sure what good that will do as the officers wont see the many other generations that have passed away. theyll just see some flea ridden kittens with a poor living area. not sure if thats enough for them to take any action as the owners can also lie and say they have a vet appointment scheduled. this family will also know it was us that reported them and this could create drama.

if i am able to report this family, what happens to the kittens if the report is successful? do they just go to council and get taken to a shelter? im worried about their safety. im in NSW, Australia btw. thank you.