A girl developed a "fixed smile" and her sister became an "elective mute" after their cruel father imposed a "brutal, strict and unbending" home regime, a High Court judge has heard.
The girls' behaviour was a response to "frightening, sadistic and violent" experiences, Mrs Justice Knowles was told.
Their father had sexually abused them; slapped, punched and kicked them; pulled their hair; made them get up very early; and sent them to bed as soon as they got home from school, she heard.
Detail of abuse has emerged after council social service bosses with responsibility for the girls' welfare asked the judge to make orders to protect them from their father.
Mrs Justice Knowles had analysed the case at a private hearing in the Family Division of the High Court in London.
The judge said, in a ruling published on a legal website, that the girls were now in foster homes and their father was serving a 22-year jail term after being convicted of a string of offences.
She had decided that the girls' father should have virtually no involvement in their lives.
Council bosses were told that they did not need to consult or inform the man about "any aspect" of the girls' "progress, development or well-being".
The judge said he should be told of any life-threatening medical emergency.
Mrs Justice Knowles said neither the girls, now in their teens, nor the council involved could be identified.
The judge said the girls' father had denied wrongdoing at a crown court trial but had been found guilty of cruelty and a number of child sex offences.
Their mother had been convicted of neglect and given a suspended prison term.
"Both girls experienced significant physical, sexual and emotional harm in the care of their parents," said Mrs Justice Knowles.
"Both girls have recounted frightening, sadistic and violent experiences and both developed a variety of behaviours to manage their experiences.
"They were hypervigilant and remain so."
The judge said one girl had become an "elective mute" and the other "developed a fixed smile".
She added: "Both girls have expressed great fear/terror of their father and both have required much reassurance that he remains in prison, does not know where they are, and would not come out of prison until they were adults."