John Hancock and Bianca Rinehart took their fight to the Western Australian Supreme Court to demand 82 documents that their mother's company, Hancock Prospecting, claimed were protected by legal professional privilege.
Justice Natalie Whitby dismissed the pair's application that asserted privilege couldn't be maintained because it was not established or had been waived.
Gina Rinehart is expected to learn later in the year if her company's stake in Hope Downs is safe. (Richard Wainwright/AAP PHOTOS)
She also reprimanded the siblings over "the nature of the applications" that were heard over six days and resulted in more than 6000 pages of court documents.
"To say that the resources dedicated to these privilege applications was grossly disproportionate to the issues in dispute is an understatement," Justice Whitby said in a 180-page ruling published late on Monday.
The judgment follows a bruising 51-day battle for spoils from the massive Rio Tinto-operated Hope Downs mining complex in WA's Pilbara region.
The complex battle that started in July pitted Mrs Rinehart's company Hancock Prospecting against the heirs of mining pioneer Peter Wright and engineer Don Rhodes amid allegations of decades-old contract breaches.
John Hancock and Bianca Rinehart were also legally represented over a claim their grandfather Lang Hancock left them a hefty share in the Pilbara mining resources he discovered in the 1950s.
The trial has also featured sensational allegations against Mrs Rinehart - which have been vehemently denied - including that she devised an unlawful scheme to defraud her children.
Mrs Rinehart, Australia's richest person, inherited her father's iron ore discovery in the Pilbara and forged a mining empire after he died in 1992.
She developed mines from tenements at Hope Downs, signing a deal in 2005 with Rio Tinto, which has a 50 per cent stake in the project.
The Hope Downs mining complex near Newman is now one of Australia's largest and most successful iron ore projects, comprising four open-pit mines.
Her wealth is estimated to be about $36 billion and she is executive chair of Hancock Prospecting.
A judgment in that case is expected to be handed down later in the year.
