Marcelino Olguin pleaded guilty Thursday to three counts of lewd and lascivious acts on a child under 14, one count of child endangerment and one count of false imprisonment.
According to the Riverside County District Attorney's Office, he will likely be sentenced to seven years in state prison and have to register as a sex offender for the rest of his life.
Olguin's wife Rosa and daughter Lennys both pleaded guilty to child endangerment and false imprisonment charges and are expected to be sentenced to four years of probation.
The story of the 13 Turpin siblings gained international attention in January 2018, when their parents David and Louise Turpin were arrested, suspected of torturing the children, depriving them of food and chaining them to their beds.
The Turpin parents later pleaded guilty to 14 felony counts and were sentenced to 25 years to life in state prison. While many of the adult Turpin siblings were free to then live on their own, the minor children were placed in the foster care system.
In April 2018, five of the Turpin children were placed under the foster care of the Olguin family.
The Riverside County sheriff's department began investigating the Olguins in early 2021. According to an arrest warrant, there were a total of nine victims; five of whom are believed to be Turpin siblings.
According to the warrant, the Olguins were aware of the "egregious, life-long severe abuses the biological parents inflicted on" them and forced the siblings to participate in a "circle confession talk."
Investigators said the Turpin children were confined to their rooms, with several of the doors equipped with door chimes to alert the Olguins when the children entered or exited.
Marcelino Olguin was accused of sexually touching the children in excess of 50 times, and told them they were "sexy, recommended they not wear undershirts... and forced kissed them and pulled a minor on top of him."
The Olguins are scheduled to be back in court for sentencing on Oct. 18.