Mr Karam filed defamation proceedings against Justice for Robin Bain members Kent Parker and Victor Purkiss for online comments they allegedly made about him.
Mr Purkiss has not been present at the hearing in the High Court at Auckland, where Mr Parker is representing himself.
Mr Karam's son, Richard Karam, gave at times tearful testimony today about the impact the "vindictive and threatening" comments had on his father.
"It got to the point that he became upset and seemed genuinely concerned for his safety and that of his family," he told the court.
Richard Karam said his company, the Coffee Guy Limited, of which his father is a former shareholder, was also harassed as a result of the comments, and the defendants urged people to boycott the business.
Joe Karam's daughter, Simone Ngaire Tatton, also gave evidence in support of her father.
"Dad has always been a man with incredibly strong values or morals ... he has always stood up for what is right or wrong," she said.
"It is easy to see how the defendants' daily comments shattered him."
The court has previously been told the comments attacked Mr Karam's motivation for supporting David Bain, who was in 2009 acquitted of murdering his parents and siblings after spending 13-1/2 years in prison.
His lawyer, Michael Reed QC, told the court yesterday Mr Karam was caused stress, anxiety and hurt.
"Without question, it has been the worst four years of Mr Karam's life."
The hearing continues.
