Gina Rinehart's lawyer has dismissed claims that the billionaire had a "cunning plan" in her dealings with the family trust.
John Hancock and Bianca Rinehart allege their mother acted "deceitfully" and with "gross dishonesty" in her dealings with the family's $5 billion trust fund, set up in 1988 by her father, Lang Hancock, to benefit her children.
They allege that in 2006, Ms Rinehart changed the constitution of the family company, Hancock Prospecting Pty Limited, in such a way as to prevent her being removed as trustee.
But Ms Rinehart's barrister Noel Hutley SC, denied the deed was changed in a way to benefit his client.
He dismissed claims that the mining magnate had tweaked the deed in her favour in a "cunning plan, worthy of Baldrick", in a sarcastic reference to British comedy series Blackadder.
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"There is absolutely no substance in any of the allegations advanced," he told the NSW Supreme Court in Sydney on Friday.
The amended deed, Mr Hutley argued, was an "exemplary example of total fairness" and reflected "complete even handedness".
Under the terms of the amended deed, the barrister explained, if Ms Rinehart wanted to "get out and retire and turn her mind to philanthropy, or the like" her children would effectively take control of the company.
He also noted that it was "passing strange" that Bianca Rinehart "seemed to be content" to sit on the company board for years under the same articles of the deed she is now complaining about.
Earlier on Friday, Judge Paul Brereton rejected a proposed replacement trustee suggested by Ms Rinehart's daughter Ginia Rinehart, who is siding with her mother in the dispute, on the basis that there was not enough time to vet the candidate.
The decision came a day after Judge Brereton rejected Bianca Rinehart's nomination to become trustee of the trust.
John Hancock and Bianca Rinehart are now expected to nominate Adelaide businessman Bruce Carter to be a replacement trustee.
If Mr Carter is not accepted, Mr Hancock will ask to be considered for the role, his barrister Christopher Withers said on Friday.
The case continues in the Supreme Court on Monday.
