Singer and former presidential candidate Dana Rosemary Scallan has denied claims that she defamed her sister and her niece.
Susan Stein and her daughter Susan Gorrell, who live in Iowa in the US, have taken separate High Court actions alleging Dana defamed them during an interview broadcast on TV3 in October 2011 during the presidential election campaign.
They claim Dana made statements which inferred both women maliciously made up claims that Ms Gorrell was sexually abused between 1971 and 1981 by her uncle and Dana's brother, John Brown.
Ms Stein and Ms Gorrell claim the abuse allegations are true.
Mr Brown, from Bracknell in Berkshire, was acquitted in July 2014 of charges of indecently assaulting two girls aged under 13 and 16 at several locations in Northern Ireland and England in the 1970s and 1980s.
He had denied the charges and was found not guilty by a jury at Harrow Crown Court near London.
He had also denied that Dana, who gave evidence in his defence, helped him to cover up the allegations.
Dana denies defamation.
She says the sexual abuse claims against Mr Brown first surfaced in 2005 during a US court dispute involving members of her family, including Ms Stein and Mr Brown, concerning copyright of her records and ownership of a music company, Heartbeat Records.
Today she made a pre-trial application for orders requiring Ms Stein and Ms Gorrell to provide security for her costs should they lose their actions.
Dana and her husband Damian were in court for the action before Mr Justice Robert Eagar.
Dana's Senior Counsel Oisin Quinn said she had a full and thorough defence to the defamation actions.
But, he said, she believed the plaintiffs would be unable to meet her costs if she loses.
She estimates the costs would be €425,000.
The plaintiffs estimate the costs at €169,000.
The court was told that Dana was asked about allegations circulating about John Brown during an interview broadcast on TV3 on 14 October 2011.
Ms Stein and Ms Gorrell say words used by Dana meant they were lying about the abuse allegations and had maliciously made up the claims.
In October 2011, Ms Gorrell made a complaint to the UK police and Mr Brown was tried concerning her claims of sexual abuse and acquitted of all charges, Mr Quinn told the court.
The security for costs application was brought on grounds including a claim neither plaintiff has assets here, he said.
In dealing with this application, the court was not required to adjudicate on the merits of the defence, he said.
There was a direct factual conflict between the plaintiffs and Dana on a key issue, he said.
Both plaintiffs claimed Ms Gorrell was abused by Mr Brown and Dana was told of that many decades ago and essentially covered it up, claims Dana has denied.
Her defence to these cases included denials the words in her interview meant what was alleged, counsel said.
She would also rely on pleas of honest opinion on a matter of public interest and on pleas of truth and justification in relation to some of the claims advanced.
In opposing the security application, both plaintiffs contend their case is in the public interest.
They also say they have "after the event" insurance cover under which the insurer will pay out €150,000 should they lose their actions but will have to pay the insurer if they win.
Mr Quinn argued such an arrangement amounts to "champerty" and is illegal here.
The relevant policies gave "huge scope" to the insurer to exit from the obligation to indemnify the insured, he argued.
The hearing continues tomorrow.