Louise and David Turpin are currently sitting in jail after being charged with multiple counts of abuse and false imprisonment of their children.
Police allege the pair locked up and starved their children, aged 2 to 29, in the family’s foul-smelling home in California for years.
Now Louise Turpin’s half-brother Billy Lambert claim the couple had planned to have another baby – making them “perfect for TV”.
He said: “Only last month Louise told me her and David were planning to have another child.”
Mr Lambert has disowned his sister following the sickening allegations brought against her and David Turpin.
The estranged half-brother also revealed he had not recently seen his nieces and nephews as whenever he spoke to Mrs Turpin on Skype she claimed the computer was broken or would make up another lie.
During several of their revealing conversations Mr Lambert claimed Mrs Turpin dreamed of making millions by starring in a reality show about her large family.
Mr Lambert said: “She used to say how they would be perfect for TV and would often mention they would be bigger than the reality show Kate Plus 8.
“She thought the world would be fascinated by their lives.
“I asked her why on earth they wanted more children and she said about wanting a reality TV show.”
But his sister’s lies and fantasies did not stop there, Mr Lambert claims as he accused her carrying out a “sham” pretence about her family’s situation.
David Turpin had been a well paid engineer but after he left his job they started to run out of money, Mr Lambert told The Sunday People.
He claims the pair lied about their financial fortunes and living in a huge house.
After a family member died Mrs Turpin called her half-brother to check on any possible inheritance, he has revealed.
Mr Lambert said: “She called to see if the estate had been sorted so she would get some money.
“For the last seven years, they carried on the pretence that David was working but it was all a sham.”
The Turpins claimed to be living in a seven-bedroom home rather than the modest bungalow where the children were allegedly found chained by police.
These money problems are said to part of the reason the mother-of-13 was so determined to have yet another child as she maintained fantasies of becoming rich from TV rights.
The family even moved to California to be closer to Hollywood hoping to mirror the career of US TV star Kate Plus 8, Mr Lambert claims.
He said: “They thought it would make them millions and household names.
“They didn’t care about the kids – it was all about them.”
Mr Lambert has said he will never speak to his sister again but hopes to adopt the three youngest children and help care for them as they are his “flesh and blood”.
His sister Teresa also hopes to adopt some of the siblings.
David Allen Turpin, 57, and Louise Anna Turpin, 49, are facing life in prison over charges including torture and child endangerment.
The arrests were made after one of the 13 siblings called police and said her 12 brothers and sisters were being held captive – with the siblings, aged two to 29, found severely malnourished in a filthy “house of horrors”.
The children were chained up, beaten and starved as punishment for doing something as simple as washing their hands above their wrists, according to police.
In further claims, the parents even left out toys they could not play with and food they could not eat to taunt the children.