The taxi burned to a shell, said Todd LeDuc, a spokesman for Broward County Fire and Rescue.
The accident Tuesday morning closed Interstate 95, the main commuter route between Fort Lauderdale and Miami, for hours, the Highway Patrol said.
Highway Patrol spokesman Lt. John Bagnardi said the taxi driver had just picked up the couples at the Port of Miami and was taking them to Fort Lauderdale-Hollywood International Airport for their flight home to St. Louis.
Investigators were still trying to determine the cause of the accident, Bagnardi said Wednesday. Witnesses had said the two trucks wound up on top of the cab after the driver of an empty flatbed truck lost control and hit a fuel tanker.
The tanker's cab burned but its tank did not, LeDuc said. The two truck drivers escaped injury.
The victims were identified as Bryant Pendleton, 42; Angela Pendleton, 41; John Madison, 49; and Frances Madison, 48, all of St. Louis; and cab driver Jean Carlos Gernier, 36, of Miami.