Police said one of the women, in her 70s, suffered serious injuries and remained in hospital. A woman in her 40s was treated for injuries in hospital but has been discharged.
Relatives are being supported by specially trained officers, police said.
Det Insp Andy Heath, of the force’s serious collisions investigation team, said: “I am saddened to confirm that a second boy has passed away.
“It is important that the family are given the privacy needed at this difficult time and my thoughts remain with them and others affected by this tragic incident.
“Investigators continue to support the relatives while we secure the evidence required in this case.”
Police have asked witnesses to get in touch.
