Inside the twisted marriage between David and Louise Turpin.

Details of the twisted marriage between David and Louise Turpin have emerged just days after the parents were charged with torturing their 13 children.

In an interview with the Daily Mail, Louise’s sister, Teresa, and brother, Billy, have revealed their older sister ran away from home at the age of 16 to be with David.

In 1984, the siblings told the news outlet, their mother, Phyllis, allowed 16-year-old Louise to date David even though he was eight years older. However, Phyllis did not tell her husband about their daughter’s relationship for fear of how he would react.

“My mom allowed Louise to date David secretly because she loved him and he was from a Christian family and she trusted Louise,” Teresa said.

That same year, David kidnapped his much younger girlfriend from school, driving her 1,000 kilometres away in an effort to elope.

"She was doing it behind my dad's back — he wasn't aware that they were dating — and then one day, David went into the high school and they let him sign Louise out of school and they ran away. He had his car and they drove.

"They made it all the way to Texas before the police stopped them."

David had persuaded school employees in Princeton, West Virginia, to release 16-year-old Louise Robinette to him without her parents' knowledge.

The police, upon stumbling on the duo, made her call home.

"My mum, who had let them date, ended up being the one telling the police they had to send her home. She wanted her home right now, but my dad said, 'No, she has made her choice, she should go off and live her life.'"

They soon married.

From the outside, Louise's siblings say, her marriage looked perfect. It was anything but.

"I just thought she had this richy life," Teresa said.

"He earned good money. The day he came and picked her up from school, I was told he told her that if she would elope with him and marry him he would give her everything she ever wanted.

"I spoke to her about some financial problems I was having just six or seven months ago and she said to me several times that [that was] one thing she could never understand."

However, the couple had declared bankruptcy in 2011.

Listen: As soon as she picked up a tennis racket, Jelena Dokic started being abused by her father. (Post continues below...)

During their 31-year marriage, the pair are said to have renewed their vows three times.

On Friday, Riverside County District Attorney Mike Hestrin laid out the charges against David, 57, and Louise, 49. They are charged with 13 counts of torture; one lewd act on a child; seven counts of abuse of a dependent adult; six counts of child abuse; and 12 counts of false imprisonment.

According to NBC News, authorities have said that the abuse the children - aged between two and 29 years old - suffered was "unimaginable".

The children were only allowed to shower just twice every year, and were given only one rationed meal per day.

"They're not being fed and they're living in these filthy, dirty conditions," Captain Greg Fellows, from the Riverside County Sheriff's Department, told reporters during a press conference.

"That's going to take its toll."

Despite taking a trip to Disneyland and visiting Las Vegas when their parents renewed their wedding vows, the siblings were largely cut off from the outside world.