Andrew Lorimer was found dead in his flat in Lurgan last year following a brutal attack.
David Lorimer described his brother's injuries: "They beat him with a hammer, they beat him round the hand, the knees and the elbows.
"Andrew had nine broken ribs, four of them broke in two places - he went through an awful death. I can't get my head round it, how horrible the death was."
During the trial, Mr Justice Weir was told that that Mr Lorimer had been left to crawl around in his flat for two days before finally "succumbing" to his extensive injuries.
Last month Christopher Wright, 22, and Richard Chester, 23, were sentenced to 10 years with five to be served in jail, while the third man, James Jordan, 20, was sentenced to eight years with four years to be spent in jail for his manslaughter.
Not happy with the sentencing, the Lorimers asked the Director of Public Prosecutions to refer the sentence to the Court of Appeal in an effort to get the jail terms extended.
In a three-page letter, Barra McGrory QC described Andrew as "an outstanding citizen" whose killing was "unnecessary and tragic".
But he said the tariffs given to the killers "are not sentences which I feel could be regarded as outside the range" for manslaughter.
Mr McGrory adds that it "would not be in the public interest" for him to refer the sentences to the Court of Appeal".
Andrew's sister-in-law Julie expressed deep disappointment at the decision.
"We felt that in Andrew's case the sentence just didn't reflect the severity of the crime," she said.
"When three people enter a man's home and beat him with a hammer, try to hide the evidence, they slandered Andrew's name, dragged his name through the muck, and tried to make him responsible nearly.
"Someone really needs to review the sentencing system, people deserve some comfort from the justice system. We got nothing."
David added: "In another three years time these guys will be out, they've a chance to maybe marry, have a family, get on with their lives, put this all behind them.
"Our Andy's never coming back. That's the bottom line, he's not coming back. And everybody's talking about Christmas, having a great time and my life has just stopped still.
"My wee brother is dead. I don't know how we are ever going to pick up the pieces."
The family have agreed to take up the Director of Public Prosecution's offer to meet them.
UUP MLA Jo-anne Dobson has criticised the DPP for not taking the step earlier and is supporting the family in their campaign.
She commented: "If he had come with me and met the family and seen the pain that they are enduring he wouldn't surely have made the decision that he made."
Julie said the whole process has "reopened all the wounds".
"How can we stand at Andrews' grave, we can't let him down. We have to keep fighting," she said.
David added: "My mother's lost her youngest son. I find it hard to even look at my mum now. I can see the pain in her face everytime that I look at her."