Pratibha's daughter, Priyanka (33), who had got engaged last month and was supposed to get married by the end of this year, was also found hanging, they said.
The victims belonged to the same family and most had lived in one home in Burari village in the northern part of New Delhi, said police officer Vineet Kumar.
Neighbours look out from a window near the building where 11 family members were found dead inside their home in the neighbourhood of Burari in New Delhi on July 1, 2018. "We can say something about the cause of death only after the postmortem reports come".
"The initial investigation, the way their hands were tied and mouths gagged, led us to register a case of murder. We are investigating from all possible angles, we are not ruling out anything", said Rajesh Khurana, Joint CP Central Range, Delhi Police.
Police said the crime scene bore no sign of robbery being a motive, with the gold jewellery the women victims were wearing undisturbed.
Sixty-year-old Partibha, daughter of Narayan also lived with the family, the dead body of 10 people were found on the first floor while Narayan's body was found in other room.
The newspaper said that at around 8 a.m. Sunday, a neighbour with whom the businessman used to go for morning walks went to see him and found the door of the house open and the 10 people, including the businessman, hanging.
News agencies quoted an unnamed police officer as saying a probe will be conducted to find "if the family indulged in occult practices" or they followed "any godman". Neighbours had not heard anything untoward, police said.
"I saw the bodies hanging, stools lying around, and my wife's aunt sprawled on the floor by the bed".
The police was investigating the case and questioning neighbours and relatives of the family.
"No father can kill his own son ... how would a mother be able to kill her own children?"
Calling it a mass murder, a media report said that it was an insider's job, who was under some tantrik's influence.
Chandrakanta, who runs a store nearby, added, "I used to run into all of them off and on".
Chief Minister Arvind Kejriwal visited Burari.
"Police are investigating ... let's wait for their investigation to be over", he said.