A male relative of the patient killed when an ambulance struck a tree was treated at scene of the accident and has been conveyed to Southampton General Hospital by ambulance.
A male ambulance crew member has been airlifted to Southampton General Hospital by the Hampshire and Isle of Wight Air Ambulance.
South Central Ambulance Service NHS Foundation Trust said it is conducting appropriate welfare checks with the families of all involved.
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A GoFundMe page was set up by the children's uncle to raise £15,000 for their funerals.
Lindsay Hoyle said his "family will never be the same" after the death of his 28-year-old daughter Natalie.