Suffolk County police in Long Island say Pauline Aluska, 54, was killed near to the spot where her brother, John Aluska, 61, died two years earlier.
Both cases were hit-and-runs. Their brother has appealed for his sister's killer to turn himself in.
In March their sister-in-law died while saving her daughter on Mother's Day.
Diane Aluska was killed after an 80-year-old driver reversed into her, moments after she pushed her 16-year-old daughter out of the way.
Diane's husband, Ken Aluska, told the New York Post that he was still mourning the death of his wife when he learned of the latest family tragedy.
"I [was] just trying to take care of my kids and get back to normal life before this even happened," he said.
"There are no words to describe it."
He added that his sister had recently retired from working at a supermarket and had planned to move to Florida.
Police told CBS New York they plan to release surveillance footage of the Montauk Highway in Lindenhurst, where the accident occurred.
"If you have a heart, if you have a soul, turn yourself in," Mr Aluska told the station, adding that he and his siblings grew up in a closely-knit family.
"Because out there somewhere, you have a family."
Police say a New York woman who was killed by a hit-and-run driver is the third person in her family to die in a pedestrian traffic accident.