The crash at about 5:30 a.m. Monday killed Alice and Bryan Young Sr. of Victorville, Calif., Trooper Melissa Matey said.
Walker said in a Twitter posting that his aunt and uncle of the same name were killed "by a drunk" at 5 a.m. Monday. The message's subject line read, "Horrible."
"We extend our deepest sympathies and prayers to Delanie and his family as they grieve this tragedy," 49ers general manager Trent Baalke said in a statement. "Our organization is here to support Delanie through this tough time, as we do with all of our players and staff. At this time, we will respect their family's privacy and ask others to do so as well."
Matey said the Youngs' vehicle was stopped on the shoulder of Interstate 10 in LaPlace, just west of New Orleans, when it was hit by a car driven by 26-year-old Nechole T. Thomas of Houston.
Her 2002 Mercedes slammed their 2012 Nissan Altima from behind at high speed, Matey said. Both cars caught fire and the Youngs' bodies were not found until the blaze was out.
Matey said it took until Wednesday afternoon for the coroner to identify the Youngs.
Thomas escaped with minor injuries and was jailed on charges of reckless driving, drunken driving and two counts of vehicular homicide -- a death involving a drunken driver. Her bond is set at $300,000.
Online jail records do not indicate whether she has an attorney.
Information from The Associated Press was used in this report.