Crystal Kuhns, 41, died Friday morning, and her daughter Mickey, 4, died Thursday evening, a Crozer Chester Medical Center spokesman said.
Earlier, authorities had identified three victims as David Kuhns, 51; Skylar Kuhns, 8; and Shawn Kuhns, 6, according to Lancaster's The Intelligencer Journal/Lancaster New Era.
Another child in the family, Kordell Kuhns, 2, remained in critical condition at the hospital outside Philadelphia, spokesman Grant Gegwich said.
The fire started in the kitchen of a three-story duplex in Lancaster, in central Pennsylvania, at about 3 a.m. Thursday after frozen potatoes were left in the oven, fire officials said.
Fourteen members of several families lived in the home, which did not have smoke detectors, fire Chief Timothy Gregg said.
One victim, Jimmie Moore, 65, was described by neighbors and relatives as a generous man and Vietnam War veteran who let another family move in after they lost their own housing.
The Lancaster newspaper reported Friday that Moore's pregnant daughter was among those who fled the flames. Martha Moore, 22, escaped through a second-floor window and shuffled across the roof to a neighbor's house.
Nearly eight months pregnant, she had an emergency cesarean section Thursday morning. Her daughter, Zaliah, weighed 4 pounds, 5 ounces, the newspaper reported.
Another person was admitted in serious condition, a nursing supervisor at Lancaster General Hospital said. Several others were treated and released.
Lancaster County coroner Dr. Stephen Diamantoni said autopsies on the first four victims were scheduled for Friday.