The medical examiner's office also said that one of the victims, Lomer Johnson, also suffered a blunt head and neck injury, which could have resulted from a fall or being hit by an object.
The other four victims were Johnson's wife, Pauline, and three of their granddaughters, 10-year-old Lily and 7-year-old twins Grace and Sarah.
All of the deaths were ruled accidental.
Stamford, Conn. fire officials said embers in a bag of discarded fireplace ashes started the fire.
The twins' mother, Madonna Badger, who is also the Johnsons' daughter, escaped from the fire. A friend and contractor who was working on the home, Michael Borcina, also escaped. Borcina was released from Stamford Hospital Wednesday morning.
Badger, a well-known advertising executive, escaped by climbing out of a window and onto scaffolding. Firefighters went into the house twice trying to rescue the victims, but they were forced out by the blaze's intensity. Four firefighters were injured, including a captain who suffered second-degree burns on his face, officials said.
Borcina and Johnson attempted to rescue their family members as well. One of the girls, found dead just inside a window, had been placed on a pile of books, apparently so Johnson could reach in and grab her after he jumped out.
Instead, authorities say, Johnson fell through the roof outside the window and was found dead in the rear of the house.
He and his wife, both of Southbury, had been visiting their daughter for the holidays.
The Associated Press contributed to this report.