Private emails between some of Gina Rinehart’s children discussing extraordinary plans to mount a legal bid against their mother almost 20 years ago have been aired in the WA Supreme Court in a high-stakes legal battle over billions of dollars in mining royalties.

Emails between John Hancock and his sister Hope Rinehart were read out on Tuesday by a lawyer representing DFD Rhodes, which is seeking a 1.25 per cent cut of royalties flowing from Hancock Prospecting’s Hope Downs mines in the Hamersley Ranges.