A teenager who survived a horror car crash that claimed the lives of her mother and brother has been dealt another tragic blow, with news her father's body has been found in floodwaters.

Khloe Heidemann, 14, was flown to a Sydney hospital with life-threatening injuries last week, after a horror crash near Berry, on the NSW south coast that killed her mother Jane Towers and younger brother Jay Jay, 12.

In further tragedy, Khloe and her older brother Shanon, 17, who lives in Queensland, have now been left orphaned, after the body of their father David was found near Gympie.

The 50-year-old was reported missing on March 30, as Queensland was lashed by the remnants of ex-Cyclone Debbie.

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He is believed to have drowned in floodwaters five days before his family was involved in a horror collision with a truck on the Princes Highway near Berry.

Ms Towers and Jay Jay were killed instantly.

Khloe remains in hospital.

The mother and her three young children had recently relocated to the NSW south coast from Queensland, following her separation from their father.

The couple's eldest child, Shanon, opted to stay in the Sunshine State with his father.

A GoFundMe page established to help the two young orphans and to pay for funeral costs has raised more than $10,000 in three days.

Sarah and Phebe Towers, Ms Towers' nieces, said the funds would help out their grandparents.

The pair said while it was not yet certain what would happen to Shanon, "if he chooses to we will take him into our home."

"This is a lot to take in within two weeks for our entire family," the pair wrote, after Mr Heidemann's body was discovered.

The pair said 14-year-old Khloe's condition was still critical.

"Our aunty and one of our cousins died in this accident, our other cousin is still fighting for her life in hospital," the said.

"So we'd like to raise money for our nan and grandad to help with the costs of the funerals and our cousin's recovery."

Ms Towers' sister-in-law Belinda Hartigan told Fairfax Media Shanon was being cared for by his grandmother.

She told the publication he was "holding up" after triple tragedy.

"He's doing the best that he can with everything that's happening," she said.