The bodies of the 4WD's driver and the husband and wife in the car were so badly burned it could take weeks to formally identify them, AAP understands. The girls were airlifted to Liverpool and St George hospitals where they remain in critical conditions.
Police visited the family's home in Ryde but, after finding no one at home, tracked down extended family members.
"Sadly those family members are travelling to the St George and Liverpool Hospitals to engage with their loved ones who are very much in a critical condition at this time," Highway Patrol Chief Inspector Phil Brooks told reporters in Sydney on Wednesday.
On Tuesday afternoon a 23-year-old woman fell from a four-wheel-drive north of Parkes.
Passing motorists treated her until paramedics arrived. She was taken to Peak Hill Hospital but she died.
Crashes have killed 21 people on the state's roads since December 15, which marked the start of Operation Safe Arrival, the state's Christmas and New Year road safety campaign.
Assistant Commissioner Michael Corboy said the deaths angered police but have made them more determined.
"We have gone from disappointed to being angry and that's an understatement," Corboy said.
"It has actually strengthened our resolve and we will be putting in place more and more police officers from now until the end of the year."
