The attack took place in Sariswa village under Majhaulia police station of West Champaran district April 19, but came to light after a case was lodged with the police.
"Three people were arrested after an FIR (first information report) was lodged on the basis of the statement of gangraped victims," Superintendent of Police Sunil Nayak told IANS.
"The gangrape was committed by four people," Nayak said. He added that three accused identified as Subhash Yadav, Suresh Yadav and Rameekbali Yadav were arrested Tuesday, while hunt is now on to nab the fourth attacker.
Police have recovered the torn clothes of the victims from the house of Suresh during an investigation.
According to police, the victims were first kidnapped and then taken to the house of Suresh where "both were gangraped by them".
The youth, whose mother and sister were gangraped, had eloped with Suresh's sister in January this year, a police official said.