Numerous erotic photos of the couple were found in the home, 20 Minuten reported, as well as photos showing the elder daughter, when she was aged between 11 to 14, nude or in her underwear. In one of them, she appeared to be sucking her mother's breast.
However, her stepfather referred to these as “simple, erotic pictures which were not shocking at the time they were made," adding that "customs have changed".
The daughter, now 23, moved out of the family home when she turned eleven but told the court that she feels traumatized.
“They had sex everywhere. In the living room, on the balcony, on their car - they never closed the doors,” she is quoted by 20 Minutes as saying. "I still remember the looks on their faces."
A spokesperson at the courthouse in Vevey, in the canton Vaud, confirmed to The Local that the case was taking place, but was unable to give further details.
The case was originally brought to court after neighbours reported the couple for suspected sexual abuse of their other daughter, who is aged eight and lives with the couple. After a medical examination found no trace of abuse, this investigation was closed, but a separate enquiry was opened into the trauma suffered by both children.
The prosecution argued that "for a ten-year period, the defendants put their personal pleasure above their children's wellbeing", saying that the girls "learned the meaning of sexual pleasure too young". The younger daughter allegedly exposed herself to a boy of her own age, which prosecutor Maria Giannattasio said shows the effects of "her parents' lack of shame".
The couple deny the allegations. The mother said: "We have never made love in front of our children. My daughter is lying. She has always lied."
The verdict is expected at the end of the week, with the couple risking up to 24 months in jail - although any sentence is likely to be suspended. The couple's defence argue that the offences were "morally reprehensible but not criminal".
Additional reporting by Raphael Warnke