A number of the reports named Yass as the town closest to the family's property, where they had been living for two years before being discovered, however the Tribune has discovered this is incorrect.

The family of 40 had been living in squalid conditions on a remote, heavily-wooded property 50 kilometres north of Yass, since 2011. The location cannot be named for legal reasons and pseudonyms have been used throughout.

It has been dubbed one of the worst cases of child sexual abuse and depravity in Australian history.

Twelve children, ranging in age from five to 15 years, have been permanently removed from the care of their four mothers, after it was found all but one were conceived by relatives, and all had experienced habitual sexual abuse at the hands of brothers, sisters, fathers, mothers, aunts, uncles, grandparents or cousins.

Three of the mothers were sisters: Rhonda Colt (47), Betty Colt (46), Martha Colt (33); the fourth mother, Raylene Colt (30), was the daughter of Betty.

The three sisters were among seven siblings who were borne of late parents Timothy and June Colt, who were brother and sister.

The inbred mothers had six, 13, six and one child/ren respectively. All of these, apart from the youngest, were fathered within the family unit according to genetic testing.

The family had been reported to community services seven times between 2010 and 2012 for allegations of neglect, failure to seek medical attention, failure to ensure children were attending school and failure to maintain a hygienic and appropriate domestic environment. Some of these reports came from a school bus driver and the local high school.

The family had relocated between states several times to avoid detection.

Police and case workers visited the farm on June 6 2012 and found four main living quarters made up of two caravans, a garden shed and another shed containing two tents.

The area was described as very dirty and littered with waste, cigarette butts and mud.

They found the children were dirty, wearing dirty clothing, had speech difficulties, poor hygiene and dental problems. There were no toilets, showers or baths in the campsite and exposed electricity wires and large bags of waste were evident within the living areas.

The family was told to clean up the site and make it child safe.

Case workers found improvements in a follow up visit on June 8 2012 but another two visits during July helped them form the view the children would be at risk of harm if they remained at the farm. They were removed July 18 2012.

But it wasn't until the children had been re-homed in foster care that the true extent of the situation was discovered. The children exhibited highly sexualised behaviour and told stories of having sex with family members.

Only the youngest child, whose parents were found not to be related, was in relatively good health and hygiene at the time of removal.

But she too later exhibited sexualised behaviour.

Some of the boys told their carers they used to torture animals at the farm and mutilate the genitals of animals.

Another girl reported having the same father as her mother and grandmother.

Genetic tests revealed eight of the Colt children have parents who were either brother and sister, mother and son or father and daughter. A further six have parents who were either aunt and nephew, uncle and niece, half siblings or grandparents and grandchild.

The mothers disputed the results of the genetic testing, saying the fathers of their children had been itinerant workers, backpackers from overseas or were now dead.

NSW Children's Court Judge Peter Johnstone ruled there was no realistic possibility any of the children could be returned to the care of their mothers safely, and placed each child under DOCs care until they turn 18.

"They were lacking basic life skills, such as the ability to shower and clean their teeth voluntarily. Their living environment was inadequate and their health and dental needs had been severely neglected. Additionally, their schooling and educational needs had been ignored, contributing to their developmental delay and deficits in intellectual functioning."

The mothers will be given the opportunity to address the sexual assault issues that precluded their ability to care for their children, but returning the children to their care was not favoured because of their reluctance to extricate themselves from the family unit.