The mishap took place last night when the Yadav family was returning after celebrating Janamsthami from Mathura to Delhi in three cars, Superintendent of Police (Rural) Brijesh Kumar Singh said.
One of the cars rammed against a stationary cantor and overturned near Jewar toll plaza.
The MP's nephews-- Arvind Yadav, Dalip, Indersen and Shambu died on the spot, while Yadav, who was in another car escaped with minor bruises.
The injured were admitted to Kailash hospital in critical condition.