Annabelle remains critical at Liverpool hospital while Jessica is at Saint George Hospital.
The actress, who played the character of Hope Morrison in the show, and her sister were airlifted to separate hospitals and are now joined by family for support.
A fire "incinerated" both cars involved in the crash after the sisters were pulled to safety.
The family's vehicle was involved in a head-on collision on the Princes Highway at Mondayong on the New South Wales south coast in Australia, with 50-year-old Craig Anthony Whitall, who was driving the other auto involved, also killed on impact.
According to New South Wales Police, the crash took place near South Sussex Inlet Road and Bendalong.
The head-on Boxing Day crash near Ulladulla left three people dead after a four-wheel-drive crossed the road and collided with a vehicle carrying the Falkholt family, police believe.
Falkholt recently filmed the fantasy film, Harmony, which is due to be released in 2018.
A 50-year-old man was also killed in the accident.
They visited the family's home in Ryde, north-west of Sydney but after finding no-one there tracked down extended family members.
"This Christmas and New Year period is meant to be a time of happiness and to spend time with family and sadly for many, this has resulted in tragedy", Brooks said.
"They're not stopping every two hours, refreshing and changing drivers, rather they're punching on to that next country town, running the risk to themselves, passengers and other road users."