When their older brother left home to live in England, never to be heard of again, their bond grew closer and stronger.
Music mogul Bruce Findlay and his brother, Brian, may have had the usual sibling spats as youngsters, but they matured to become friends as well as brothers.
Now they share a brotherly bond that's far more than simply skin deep, thanks to a touching gift of life that means this Christmas will be a family celebration like no other.
Brian, 74, is today fighting back to full fitness following a transplant operation in July that saw him receive one of his brother's kidneys.
Since then the pair have extended their brotherly bond by taking leading roles in a new NHS campaign aimed at encouraging more people to register as organ donors.
While Bruce's links with super group Simple Minds meant the operation made headlines at the time, they only scratched at the surface of the deep bond that ties the brothers.
It's only now, as both continue to recover, that the enormity of what they've been through has hit home.
"I think at the time we were a bit flippant and sanguine about it all," explains Brian, who lives with wife Maureen on Queensferry Street. "I just wanted it over and done with and to get my life back.
"But recently it's gone through my mind many, many times.
"What can I say to him that can show how grateful I am?"
Indeed, finding the right words to sum up his feelings is a struggle, even though the pair are now closer than ever.
"We're both sentimental in some ways but we've never been the kind of brothers to be crying on each other's shoulder, but we've always known that we are always there for each other.
"The seriousness of this and the importance of what he's done has hit me more and more as time goes on," he adds.
"To be honest, there aren't really words to express how I feel."
The kidney swap set a poignant seal on a close relationship that has endured down the decades.
The brothers were still young when their parents divorced - a rare event in the early 1950s - leaving their mum to raise them and their older brother, Rory, alone.
The pair were living in Falkirk when they launched the first of a string of record shops that would change the face of Scottish music scene.
Bruce's became synonymous with cutting edge music. For thousands of 1970s and 80s teenagers, the brothers' music shops were essential meeting points to pick up the latest vinyl and carry it home in an "I found it at Bruce's" bag.
"Because Brian's eight years older than me, I suppose I saw him as a bit of a father figure," says Bruce.
"When I was ten, he was 18 and making money and I looked up to him.
"When we went into the record shop business, opening Brian Findlay's record shop in Falkirk and then Bruce's in Edinburgh in 1969, not for a moment did we think it would become a phenomenon."
Their bond was strengthened by the disappearance of their older brother, Rory, who left for London in the late 1960s and was never heard of again.
"He would be 76 now," adds Bruce. "We don't know where he is, which is regrettable and sad."
The shocking death of their mum from oesophageal cancer, aged 56, just a week after their business was launched, was also heartbreaking.
"I was 23 at the time," recalls Bruce. "She died very suddenly, choked to death.
"We were both devastated. I suppose all those things happening make you appreciate the family you have got."
The pair set up a chain of Bruce's record shops, but as larger chains muscled in to copy their format, running an independent chain became more difficult.
They were taken over by Guinness but Bruce became disenchanted and instead launched his own record label, Zoom, and took on unsigned Glasgow band Simple Minds while Brian pursued a career in catering.
Brian's health took a turn for the worse four years ago when his ankles suddenly started to swell, a common sign of water retention which often indicates kidney trouble.
His condition deteriorated and he became more breathless and needed lengthy spells of kidney dialysis.
Doctors warned earlier this year that his kidneys were failing and he needed a transplant.
"When my brother phoned and said he needed a transplant, I said right away, ‘Have one of mine'," says Bruce, who runs Schoolhouse Management which includes looking after Scottish electric folk band Aberfeldy.
"I wasn't really thinking about it too much, but I reckoned I was fit enough. I definitely meant it. Two or three friends and family also volunteered.
"A month later, he said, ‘Are you serious?' and I said, ‘Of course I am. I'm deadly serious'. I had no doubts at all." Bruce was warned that the operation, although one of the most performed of transplant surgeries - the first kidney transplant in the UK was performed in Edinburgh exactly 50 years ago this year - was still not 100 per cent guaranteed to work, and that complications could arise.
But the warnings only made Bruce more determined to push on.
Now Brian, who runs The Deacon House Cafe, situated off the Royal Mile, thinks they both reverted to their youth and simply didn't allow themselves to dwell on potential problems.
"I think we forgot for a bit that he's 66 and I'm 74 and that maybe things might not go smoothly. But, in fact, that probably was a good thing because we didn't waste energy worrying either."
Surgeons at Edinburgh Royal Infirmary performed keyhole surgery to remove Bruce's kidney while, in another theatre, medics prepared Brian for the more complex process of receiving it.
Within hours the two brothers had come through the procedure and the impact on Brian's health was immediate.
As it turned out, it was Bruce who endured complications when he developed an infection which meant he had to stay in hospital longer than originally planned.
"I developed a slight infection," he explains.
"It was nothing to get upset about. To be honest, it was more of an inconvenience than anything else. It happened, it was treated and it was fine."
Since then, the pair have been carefully monitored and in spite of some minor teething problems with Brian's new kidney and Bruce's remaining kidney having to work harder, all has gone well.
Now they are determined to encourage others to consider the registering to become organ donors.
The Lothians already has one of the highest numbers of people on the register in Scotland, but the local health board wants to increase the number from 42 per cent to at least 50 per cent of the population.
NHS Lothian has been asking businesses, various organisations and universities to help increase the number by encouraging staff to learn about organ donation.
"I love the NHS," says Bruce. "The staff, the nurses, the doctors and the surgeons are fantastic.
"Doing this for Brian was a no-brainer," he adds.
"After all, he is my brother."
For more information visit www.nhslothian.scot.nhs.uk/signuptosavealife or text "fifty" to 61611.