The couple, who were arrested just over a week ago after on their 13 children escaped from the family home and called police to report that she and her siblings were being held captive and tortured. Authorities raided the home and found the couple attempting to untie several children who were found shackled to beds.
Both David and Louise have pleaded not guilty to nearly 40 offences, including torture, false imprisonment and child abuse.
Louise's sister, Teresa Robinette, appeared on Megyn Kelly Today to shed light on her sister.
Robinette claims she was unaware the children were being held against their will, but she did admit to knowing that her sister and her brother-in-law had begun to engage in 'deviant sexual behaviour.'
Teresa told the host: 'At the time, she said...that the older children were helping take care of the younger children so her and David could sow the wild oats they didn't sow when they were younger.'
Robinette then goes on to explain that her sister called her for the first time when they she and David went to a bar and got drunk, but then the phone calls got more disturbing.
In 2009-2010, Terese says that she received a call from her sister where she was told of one of her sister's 'plans' to sleep with a man she met online, with David's permission.
'It was a very weird thing to me, that I would never do,' Robinette said.
'She told me that her and David had met a man online from Huntsville, Alabama. And they were on their way there to meet him and that she was going to sleep with him. And that David was okay with that.'
Robinette said she told her sister she thought she was making a mistake, but that Louise went through with the plan anyway.
'What makes it weirder, is exactly one year to the date of the anniversary she did that, she called me and thought it was funny that David was taking her back to the exact same hotel room, the same everything, the exact same bed she slept with this man in, so that David could sleep with her in the same bed.'
The Turpin children range in age from 2 to 29 and sources told Crime Watch Daily that police are allegedly conducting DNA testing to make sure the siblings are all related.