Police said Stephenson and his three passengers -- Maryanne Stephenson, 29, Brian Stephenson, 66, and Sheralyn T. Stephenson, 56, -- died at the crash scene.
First responders used the Jaws of Life to remove the victims' bodies from the wreckage.
Walsh was taken to a hospital with non-life-threatening injuries, Hutchinson said.
Investigators believe the Stephenson family was returning to a rental home in Davenport after visiting the Kennedy Space Center when the crash happened.
Police said GPS in the car instructed Adam Stephenson to make a U-turn at the intersection likely because a crash was blocking Challenger Memorial Parkway, which was part of his planned route home.
The crash remains under investigation.