Family members said the boys, three of whom were 38-year-old ex-firefighter John Heller's nephews, were spending the night at Heller's apartment building in Oneonta when the fire broke out around 4:20 a.m. Saturday.
Relatives have posted online that Heller got his fiancee and all the boys out of his burning third-floor apartment but didn't make it out himself. Oneonta Fire Chief Patrick Pidgeon confirmed Heller's death Monday but said no cause had been determined.
One of the boy suffered burns on his arm, according to Erika Heller, John Heller's sister-in-law and mother of three of the boys.
"John Heller has passed because he was saving my children and the love of his life," she wrote.
Heller was a part-time Oneonta firefighter from October 2003 to August 2009, according to Pidgeon.
The cause of the fire was still being investigated Monday, the fire chief said.