Sarah Wolfe, 38, and Susan Wolfe, 44, were discovered in their home, both dead to a single gunshot wound to the head.
Police found a car, the sisters' lime green Ford Fiesta that had been missing since the sisters were killed, after 1 a.m. Saturday.
The Allegheny County Medical Examiner's office said Monday the deaths had been ruled homicides, but police said they have no yet identified a motive or suspect in the crime.
The victims were the sisters of Rep. Mary Wolfe, D-Iowa, who on Facebook thanked friends and neighbors for their condolences.
"We are so grateful," she wrote. "Heartbroken, but grateful."