It is difficult to imagine they came from the same area, never mind the same family. Dermot Fitzpatrick wears sports tops that hang on his gaunt frame and tattooed arms. His brother wears a suit jacket, opennecked shirt and wire-framed glasses.
The difference is heroin. Dermot talks about his time in the separation unit of Mountjoy and his brother tries to remember where it all started to go wrong.
A Needle And The Damage Done, a documentary to be shown on RTE next Thursday, tells the a story of one man's drug abuse.
There is no narrator. Dermot sits in his pristine bedroom, in front of satin rouched curtains, and talks about his days of robbing and violence. The programme opens with a shot of the long grey wall around Mountjoy Prison.
It was like Heuston Station at rush hour - all the time, he says, sitting on a canal lock outside the wall. "There was just roarin' and keys."
"It's a very impressive place, particularly this place here the separation unit, where I spent six and a half years. It's a very confining place so it's brilliant to be able to sit here lookin' over at it." There is a quick run-through of the family history. One of 12, he was into hiking football and canoeing, he tells the camera. He was closer to his Da than his mother - "Me mother's me mother" - as a child.
Downstairs in her pristine kitchen Dermot's mother talks about how her husband made excuses for Dermot as he got into trouble.
He was "a very loveable lad", his mother in a voiceover says, as Dermot swallows a range of pills she hands him.
She found out her son had a heroin habit when she found a syringe in his pocket, he says. He had been out robbing and had thrown his clothes on the floor for her to wash. But instead of hearing this from her we hear it from Dermot. The effect on his family is only touched on.
"Hurting me mother was the worst thing that Dermot did," his brother says. "He robbed people, he robbed banks, he hurt people when he was robbin' banks," he says as if it is something he is still coming to terms with.
The spiral of chaos is familiar to anyone who has heard a junkie's story. The stealing starts small and the more money they steal the more drugs they take. The more drugs they inject the more drugs they need and the more money they steal. Dermot Fitzgerald graduated along the usual career path, staring off with handbags and finishing with armed robbery.
It is difficult to escape from the typical tale, when these stories are told. The documentary never really explains what those days must have been like.
The closest it gets is when Fitzpatrick describes an addict as being "like a hyperactive child, constantly on the go, whether you're on the run from the police, whether you're goin' out robbin' or going out to score drugs or whatever."
The voices of the victims of Dermot's violence are never heard.
Producer Michael O'Kane explains that the original idea was to tell the story of a victim of crime and their attacker. But he could not find people willing to tell their stories.
Now working for the Pathways Project, which tries to reintegrate prisoners into society, Dermot says he agreed to do the documentary for various reasons. "I felt there were some important issues and incidents in my life that I felt needed to be heard, like when I was told I had HIV, the support I had from my family when I was locked up."
He hoped to "get the message across to the younger generation" and yet on camera his view of their future is bleak.
In the pub one of his friends calls him Dr Know when he tells them his medical results were good. If he knew then what he knew now he wouldn't go on the gear, he says. "Bollocks," his friend snorts.
He shrugs and admits his friend knew nothing about HIV or hepatitis and yet he did not start taking heroin. "We came from same areas: you didn't, I did - I don't know. I think you'd need a psychologist to work it out."
A Needle And The Damage Done will be shown next Thursday at 8.30 p.m. on RTE 1.