The incident happened in east Delhi's Gokalpuri area Saturday early morning.
"Arun Chauhan first killed his wife Kavita, 35 and asked his landlady to call Akash, 22, who was her nephew, on the pretext of searching for his mission son. He stabbed Akash around ten times and then fled," a police officer told IANS.
Akash, who was recently selected as a head constable in the Delhi Police, was rushed to the hospital where doctors pronounced him brought dead, said the officer.
Police said Chauhan and Kavita had been living with their two children - Pintu and Khushi - at a rented flat in Gokalpuri for the past few months. Akash also lived in the same locality.
A neighbour told police that the couple had a fight over some issue Friday.
Police were informed about after Kavita's daughter spotted her body inside the house. While the police were carrying out their investigation at Kavita's house, they were informed about Akash's death.