Ramesh (60) and Poonam (27) were charred to death while Ram Singh (50) and John (55) suffered minor burn injuries in the incident.
Ramesh was said to be mentally challenged while Poonam could not have run away as she had some severe disease in her legs, officials said.
According to Delhi Fire Service, the fire broke out around 2:30 AM when the temporary shelter of around 150 homeless people which housed senior citizens, mentally challenged people and others.
Initial inquiry suggests that the fire started with a short circuit causing an explosion in a cooking gas cylinder which further fuelled the fire.
The old age home was run by an NGO Earth Saviours Foundation, it was a makeshift shelter made of tents and it was being run in the area for over five years.
"After the fire, at least 20 people residing in the old age home left the place. Its residents have been given shelter in an open park nearby and the remaining tents," the official added.