They had even made Naomi Ilonga, 19, cut her long hair to “release the witchcraft”, jurors were told.
Eric Bikubi and his partner Magalie Bamu, both 28, deny murdering Bamu’s brother Kristy, 15, who drowned in a bath at the couple’s flat on Christmas Day 2010.
The prosecution says Kristy and his two brothers and two sisters were beaten and terrorised for four days at the flat in Forest Gate, east London.
They had been accused of being witches and sorcerers after arriving from their home in Paris to spend the festive season with the family.
Kristy, his sister Kelly, 20, and an 11-year-old sister were accused of influencing another child in the family.
Jurors heard Kristy was tortured with “an armoury of weapons” and had 101 injuries before being placed in the bath of water where he “begged to die”.
Brian Altman, QC, prosecuting, said family friend Naomi stayed with the couple for a month in August 2008.
He said: “Bikubi accused Naomi of having got witchcraft because she would bite her nails.”
Bikubi has pleaded guilty to Kristy’s manslaughter on the grounds of diminished responsibility, but this is rejected by the prosecution. He has admitted assaulting Kristy’s sisters.
Bamu denies all the charges, but is accused of taking part in the abuse. The trial was adjourned to Monday.