The two were murdered at Chandelamal village yesterday.
The girl's father Mukesh and brother Deepak have been arrested, SP Ajay Bhushan said here.
They allegedly confessed to killing the couple for "tarnishing the family's name".
The victims' bodies have been sent for post-mortem and security has been tightened in the village, police said.
The incident comes after a 16-year-old boy, Irshad, was found murdered allegedly by two brothers who suspected him of having an affair with their sister in Kawal village of the district.