The crash involved a Chevrolet Captiva, a Ford Mondeo and a Honda Civic.
A man in his 70s and a woman in her 60s remained in a life-threatening condition, police said.
A man and woman in their 30s and a five-year-old boy had suffered serious injuries and were in a stable condition, they added.
Sgt Wragg thanked members of the public who had provided first aid at the scene.
He said: “We are continuing to investigate the circumstances of the collision.
“I would ask that anyone who witnessed the incident, or may have seen any of the vehicles just prior to the collision, to please contact us.”