One of the suspects, Terry Ballard, 26, was a grandson of a close friend of the victims and lived near them in the Strawberry Mansion neighborhood. The other, Justen Smith, 19, is from Glen Campbell, a hamlet in western Pennsylvania.
One of their children found the bodies of Rufus Perry, 79, and his wife, Algladis, 66, in their home last week. Investigators originally said they might have died of natural causes or accidental carbon monoxide poisoning, but then ruled the deaths a homicide.
Homicide Capt. James Clark said Ballard and Smith were arrested after a neighbor said the two young men were in the Perry's yard the day they died. Both allegedly confessed during questioning.
Ballard and Smith said Algladis was strangled and smothered after she caught them stealing money, Clark said. Her husband tried to help her and was also killed.
The pair allegedly stole $120 and a gold chain.
Neighbors said Ballard is from a "good family."
"She lost her best friends and now her grandson, over a senseless killing," a man who did not want his name used told the Philadelphia Daily News. "I know she's hurting. This is bringing shame on his grandma's people."