Awadhesh Kumar, aged 18, was allegedly assaulted by his father Kailash Nath after which the teenager fell unconscious in his home last night, they said.
When Awadhesh's mother Munnu Devi and sister Nisha tried to rescue him, Kailash assaulted them as well, police said.
Later, Kailash locked them in a room and set it on fire.
Munnu Devi and Nisha managed to escape but Awadhesh perished in the fire.
Kailash also suffered burn injuries and was admitted to a hospital, police said.