Further details have emerged following Saturday's crash on the M5, which claimed four lives.
The motorway in South Gloucestershire was shut after a van travelling south crashed through barriers and collided with two vehicles heading northwards.
Police said one of the victims was travelling in a Seat Leon and three others in a second car, the details of which cannot yet be released.
Three others remain "critical but stable" in hospital.
They are a 42-year-old woman, a 12-year-old boy and a 10-year-old girl.
"A full investigation is being carried out into the circumstances of this collision, which involved a Mercedes box van and two cars," an Avon and Somerset Police spokesman said.
"Our thoughts remain with the families of all the victims of this tragic incident.
"[The] investigation will involve a thorough examination of all the vehicles involved and we're working closely with the Driver and Vehicle Standards Agency (DVSA) to progress these enquiries," the force spokesman added.
The van driver, a man in his 40s from Worcestershire, has been spoken to by collision investigators.