Both were transported to Gwinnett Medical Center in Lawrenceville for treatment.
James Turner died several hours after the crash and his wife died Sunday, Washington said.
Benganovic faces between three and 15 years if indicted and convicted of vehicular homicide in the first degree, Washington said, but the district attorney and a judge will make final sentencing decisions.
The 17-year-old is also charged with reckless driving, failure to obey stop sign, failure to maintain lane and serious injury by vehicle, which would likely be dismissed if he is indicted on the homicide charge, Washington said.
Beganovic bonded out of jail on Saturday shortly before midnight.