Members of Dana Rosemary Scallon's family allegedly supported false allegations of sexual abuse against her brother to derail her election campaign following a bitter inheritance feud, a court heard.
Former MEP and Irish presidential candidate Dana allegedly told her sister Ellen "you don't know anything you stupid b***h" when she was asked to settle the row.
John Brown, a brother of the singer-turned-politician, faces five counts of indecent assault in the 1970s against two girls under the age of 16, who cannot be identified for legal reasons.
Harrow Crown Court heard how the historic allegations against the 60-year-old had effectively split the Scallon family in two.
One of the alleged victims, now 47, claims John Brown touched her inappropriately on four occasions in the UK and US.
Her claims are being supported by Dana's brother Robert Brown and her sister Ellen Bradley, both of whom gave evidence in court yesterday.
But defence barrister Martyn Bowyer, representing the accused, said their testimony was concocted to get their own back at Dana and John Brown in a row over the inheritance of their mother's house.
Robert Brown told the court he first heard about allegations against John Brown in 2003 around the time Dana first ran for the presidency of Ireland. He claimed he subsequently confronted the defendant during a phone call a short time later.
He said: "I said to him 'if there is any truth in this then you need to go to the USA and deny it. It will destroy the family name and it will be dreadful for Dana's campaign. The anti-abortionists would love to get hold of this and it will get back to Ireland', but he wouldn't do it."
Addressing Robert Brown, Mr Bowyer suggested he had subsequent contact with Irish Independent journalist Greg Harkin, who is due to be called as a witness in the case, with the intention of getting the story aired.
He said: "You're suing him because you believe he is doing you out of money from your mother's house.
"I'm going to suggest to you that, along with your sister (Mrs Bradley), you were happy to allow this story to come into the press and it may very well be that the target was your sister (Dana).
Robert Brown denied the accusations from Mr Bowyer and insisted the phone conversation with his brother John had taken place.
Mrs Bradley told the court she first heard about the allegations in 2004 when she overheard an argument involving the alleged victim's father and mother at a studio in the US.
She gave the court a similar account of the row as the mother of the alleged victim did earlier in the case, leading defence barrister Mr Bowyer to question whether they had been in contact this week.
Mrs Bradley was asked if she had ever said she had been "swindled out of an inheritance" by her brother John, which she denied.
He went on to say: "Because of this dispute with John Brown and your closeness (with the alleged victim's mother), you have fallen firmly in her camp."
She said through tears as she sat in the stand: "I was not in anyone's camp. My mother used to say 'stay out of it' and I'm trying to do that. I said to Dana 'you need to sort this out . . .' and she said 'you don't know anything you stupid bitch'."
The hearing continues today.