The body was recovered from their house in Naihati town after area residents complained to police about a stench emanating from the dwelling.
Sharbani Pal, aged around 60, was residing in the house along with her brother Amarnath Pal, 64.
The cause and time of death would be known only after a post-mortem, a police official said.
In a similar case reported in 2015, Partha De, 44, was found living with the bodies of his sister, father and pet dogs for almost a year at the family house on Robinson street.
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