Within a few days, Shanon and Khloe Heidemann lost both their parents and their little brother in two separate, tragic accidents.

The teenagers’ father, David Heidemann, 50, was last seen on March 31 after leaving his home in Mondure, Queensland, and disappearing in the havoc wreaked by Cyclone Debbie, according to Nine News.

Shanon, 17, was helping search for him in floodwaters when his mother’s car collided with a truck at Berry, on the New South Wales South Coast on April 4.

Jane Towers, 39, and her 12-year-old son Jayjay died, while 14-year-old Khloe was hospitalised with critical injuries.

She remains comatose in The Children’s Hospital, Westmead, with two fractured legs, a fractured arm, shattered pelvis and brain swelling.

Just four days after the car accident, David's body was found in Barambah Creek by Queensland Police.

The couple were separated and Shanon lived with his dad, but will now be cared for by his grandmother.

A family member, Belinda Hartigan, told the Sydney Morning Herald he was "holding up" as best he could.

"The family is grief stricken and utterly heartbroken," Mrs Hartigan told the newspaper.

"Their loss is unbearable."

She described Jane as a "little ray of sunshine" and said before they split up David and Jane were "a lovely couple".

Her daughters have launched a fundraising page to help cover funeral costs.