THE twisted brother and sister at the centre of an incestual Australian family-of-40 had four kids together, reports claim.

Martha and Charlie Colt were among the eight relatives arrested when they were found living on a filthy plot which "smelt of urine in faeces" in April.

Genetic tests found 11 of the 12 kids, who slept in squalid tents without running water or electricity, were born to parents who were related.

The children, aged between five and 12, could not speak properly and had deformities associated with inbreeding.

Now it has emerged that sick siblings Martha, 38, and Charlie, 45, shared a "marital bed" when they were arrested in New South Wales.

Martha, a pseudonym to protect the identity of child victims, and brother Charlie were living in the town of Griffith at the time, a court heard.

Martha was charged with perjury while Charlie is accused of more than a dozens offences including six counts of sexual intercourse with a child under 10.

Cops said four of Martha's five kids, aged between 11 and 20, were born as a result of intercourse with a direct parent or more likely her sibling, Charlie, news.com.au reported.

Central Local Court also heard that police are seeking further DNA samples from members of the Colt family before charges laid against them can proceed.

NSW Police child protection squad detectives swooped on April 15, arresting eight members of the Colt incest family across three states.

Stunned detectives and welfare authorities found 38 members living on the filthy property which had no running water, electricity or proper sanitation.

The children did not know how to use toilet paper, a toothbrush or shower, and had bed-wetting and hearing problems.

They were years behind at school (if they had attended at all), tortured animals and had sex with their cousins, uncles and aunts.

The charges were brought five years after police raided the Colt's incest bolthole hidden in the hills behind the rural town of Boorowa in 2012.

Martha's alleged offences are fewer than some of her co-accused siblings and nephews who face charges of sexual intercourse with children, indecent assault and incest.

Derek Colt, 29, faces two charges of incest with a person under the age of 16 while Raylene Colt, 34, and 50-year-old Betty face perjury charges.

The Colt family originated in New Zealand with Tim and June marrying in the mid-1960s before emigrating to Australia. Betty is believed to be their child.

The clan spread to remote parts of Australia after the NSW farm was raided in 2012. Detectives on Friday wouldn't confirm if any of the removed children had since returned.

At Martha Colt’s second bail application on Wednesday, Magistrate Alison Viney heard that the accused had high blood pressure and had suffered chest pains and migraines in prison.

She had also fallen from an upper prison bunk and suffered soft tissue damage, and was finding her first time in custody “overwhelming”.

If released, she would have to rely on Centrelink welfare payments for her rent, and intended returning to Griffith to live.

Prosecutor Katharine Jeffreys told Ms Viney that a previously unsuitable address had not been the only reason Martha Colt had been refused bail in April.

Ms Viney said there was a risk Ms Colt “could abscond to seek solace with other family in another state”, and refused her bail.

Ms Colt swallowed, bowed her head briefly and looked at her hands.