Jones said the fourth child, Ladell, remains at the hospital in critical but stable condition.
Jones said that the family received word that Kyair died yesterday morning. Kayell died on Sunday and Laniyah on Saturday, she said.
Autopsies have been performed, but the results have not yet been released to the family, she said.
"It was just so many things," Jones said of the babies' conditions.
Jones said Laniyah, who appeared to be the strongest of the four, had blood on the brain. One of the boys had a hole in his heart, she said.
At the time of their birth, three of the infants weighed more than two pounds, while Kyair weighed about 1 pound, 14 ounces.
The quadruplets were born with underdeveloped lungs, which is common for babies born at 28 weeks. All four were to remain in the hospital until November - Green's due date - for monitoring.
Funeral arrangements are pending.
"It's hard, but we're doing OK," said Jones.
Green did not use fertility drugs. Both Green and the infants' father - Ladell Ramey, 22, also of Philadelphia - come from families with sets of twins.
Ramey's mother and father are each a twin, and both of Green's grandfathers are twins.
Jones said that her daughter, who was released from the hospital in late August, was doing better than expected, but that the stress of the delivery and the deaths of three of her children are taking a toll.
"Of course, as a parent, as a mother she's not taking it very well, but she knows she has to accept it," Jones said.
Contact staff writer Lloylita Prout
at 215-854-2877 or firstname.lastname@example.org.