Gina Rinehart's son John Hancock called his youngest sister "an oxygen thief", a Sydney court has heard during the latest battle over control of the family's multi-billion-dollar trust.

The youngest Rinehart, Ginia, has sided with her mother against her siblings and the NSW Supreme Court yesterday heard that Hancock had expressed contempt towards her.

But Bianca Rinehart, who temporarily fell out with Hancock, defended his comments despite telling her mother in 2004 she was "deeply concerned about [his] reckless bite-the-hand-that-feeds-you approach".

"[It's] not a personal attack," she told the court.


She added that her brother's drinking and gambling problems had been "damaging in the past".

"He doesn't want to see the family business left in the hands of someone ... he feels isn't up to the job."

And the contempt Hancock had for Ginia was born of worry about who would be "assuming real and great responsibility of taking over the family company", Bianca Rinehart said.

She and Hancock have since reconciled, with Hancock backing her bid to take charge of the family's A$5 billion ($5.4 billion) trust.

Ginia was not the only one who angered her older brother.

Bianca, Gina Rinehart's eldest daughter, said her younger sister Hope Welker "was pretty much at her wits' end" and felt "kicked in the stomach" after the way she was treated by Hancock.

"All I feel is pain and anxiety. You are kicking me in the stomach," Hope emailed her brother in February 2013, Bianca Rinehart told the court.

Welker has withdrawn from the debate, distressed at the way it was proceeding, and dealing with her own divorce.

Hancock and Bianca Rinehart allege their mother acted "deceitfully" in her dealings with the trust, set up in 1988 by her father, Lang Hancock, with her children as the beneficiaries.

So far, every proposal for a replacement trustee - including Bianca Rinehart, Hancock and independent trustees - has been rejected during lengthy court proceedings.