The incident was reported to the police after neighbours noticed foul smell emanating from the house where the duo stayed.
The deceased, Rajender Kumar Bhatnagar, 68, was a teacher in a private school.
The younger brother died about a week ago, but his elder brother could not inform anyone as he was not in a mental condition to do so, the police said.
They were unmarried and the police are trying to trace their family members, they said.
An autopsy was carried out and prima face, it appears that it was a natural death.
The elder brother is being examined by doctors.