Sister of House of Horrors Mom Says They Were 'Trained to Keep Secrets' Growing Up

Oxygen's two-hour special The Turpin 13: Family Secrets Exposed, hosted by Soledad O'Brien, delves into Louise and her husband David's troubled 30-year journey

The sister of accused child torturer Louise Turpin says they were “trained to keep secrets” when they were growing up, according to an upcoming TV special that will examine the California house of horrors case that first broke into the headlines three months ago.

The two-hour The Turpin 13: Family Secrets Exposed, hosted by Soledad O’Brien, delves into the troubled 30-year journey of Louise and her husband, David Turpin — from West Virginia, where they met, then to Texas and finally to Perris, California where they were arrested in January for the alleged abuse, torture and imprisonment of their 13 children, who ranged in age from 2 to 29.

In a trailer for the special, O’Brien asks Louise’s sister Teresa Robinette how such suspected violence, which prosecutors believe got worse over time, was kept hidden for so long.

Robinette, who has repeatedly spoken out about the case, says that secrecy was not unfamiliar to their family.

“Since we were very little girls, we have been trained to keep secrets and be quiet,” she explains.

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David, 56, and the 49-year-old Louise, who have pleaded not guilty to the many charges they face, are in custody awaiting a preliminary court hearing scheduled for May.

They face up to life in prison if convicted on all charges.

In March, the Turpins’ seven adult children were quietly discharged from California’s Corona Regional Medical Center, where they had been taken for treatment after their parents’ arrest. (The six younger children were treated at a separate facility.)

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From the hospital, the older kids reportedly moved to a new home in an undisclosed rural part of the state where they plan to get their GEDs and attend college.

“It is pretty new and different and I think quite extraordinary to have some freedom, really for the first time, and experience life outside the type of constraints they had experienced,” Caleb Mason, an attorney for the seven adult siblings, previously told PEOPLE. “It is an extraordinarily positive thing for them and it will take some time to get used to, which is another reason we are trying to keep this transition at a slow and steady pace.”

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The case first came to light in January after the couple’s 17-year-old daughter climbed through a window and, using a cell phone, called 911, authorities have said. The teen said she and her siblings were allegedly being abused and held captive by their parents.

Responding officers found what they have called a scene of malnutrition and squalor at the Turpin residence, with some of the children chained to the furniture. Prosecutors allege the parents beat, strangled and starved the kids in an intensifying cycle of abuse dating back to at least 2010.

Also interviewed for the Oxygen special is Louise’s half-brother, Billy Lambert, the family’s neighbors as well as child trauma and law enforcement experts.

The Turpin 13: Family Secrets Exposed airs April 28 (6 p.m. ET) on Oxygen.