PHILADELPHIA — Two teens accused of fatally shooting bystanders during Saturday’s mass shooting on South Street were taken into custody Thursday by US Marshals in Richmond, Virginia, the Philadelphia district attorney’s office said. Qaadir Dukes-Hill, 18, and Nahjee Whittington, 17, are expected to face murder charges after being extradited back to Philadelphia, District Attorney Larry Krasner said during a news conference at his office. Dukes-Hill is accused of shooting 24-year-old Alexis Quinn, a home health aide, while Whittington is accused of shooting Kristopher Minners, 22. Both of the v…