The children - who were taken into care after social workers in Ashington, Northumberland, found them living in squalor - were said to be so neglected they did not know what a proper meal was.
Christopher Knox, for the prosecution, told Newcastle upon Tyne Crown Court that the girls grunted like animals and 'were complete strangers to the bath'.
Mr Knox said: 'The foster mother they were taken to described the physical condition of the two girls as disgusting. They were dirty and riddled with threadworm.
The girls, who were 2 1/2 and six years old when they were taken into care, had no form of linguistic communication.
One of the sisters, who cannot be named for legal reasons, began to simulate sex acts while staying in care and was often seen trying to stimulate herself. She later disclosed that she had been subjected to abuse by her father. Further investigations revealed instances of sex abuse relating to other children.
The 41-year-old father, admitted two specimen charges of indecent assault, two charges of indecency with a child, assault occasioning actual bodily harm and child cruelty. His 40-year-old wife admitted child cruelty. Sentence was adjourned for reports to be prepared.Reuse content