The brothers and their 53-year-old mother were arrested yesterday after the two sisters approached a resident, who runs an NGO, later informing the police about the incident, Wadala Truck Terminal police station's senior inspector Suhas Garud said today.
"Both the girls, one of them a minor, have been sent for medical examination," Garud said.
According to the preliminary probe, the mother forced the girl to have sex with the brothers. She also tortured the girls and warned them not to reveal their ordeal to anyone.
A local court today remanded the three accused in police custody till April 27, the police officer said.