"That's a good question," laughs their father, Brian Evans, a former professional golfer who runs the Pinheiros Altos club in the Algarve, when I ask about Thom's year out from the game, spent singing with former schoolmates in the boy band Twen2y4 Se7en. Their mother, Sally, a one-time 100m sprint champion in Natal province, South Africa, points to her mother and aunt, who were both choral singers. But it will be the brothers' sporting prowess that Scotland supporters will be looking out for in Paris, and that definitely comes from close family.
The couple are speaking from Barbados, where they are on holiday. Brian flies to Paris tonight for the match – "we're incredibly proud of them already, but this is really going to take the cake" – and, back in Barbados, Sally will be glued to the television to watch her sons become the 20th set of brothers to take the international field in the same Scotland team (a further 24 sets of siblings have played for Scotland, but not in the same match).
Max (25) and Thom (22) are both formidable players, currently with the Glasgow Warriors, and both played their part in Glasgow's defeat of Toulouse in the Heineken Cup last month. They are also golfers, with Max having gained his professional qualification in Portugal during a spell out of rugby.
They grew up in Portugal, but their rugby was seriously nurtured at their boarding school, Wellington College in Berkshire, where Sally's Glasgow-born father, Fred Thom, who lived nearby, would shout encouragement from the sidelines. "I'm proud and happy," Sally says of her sons' double debut, "but I'm a bit sad too that my parents aren't around to see it. My father loved his rugby, and although he emigrated to South Africa after being demobbed from the Royal Navy after the war, he always maintained his Scottish roots."
Asked about the nurture/nature balance, she reckons it's a bit of both: "We've always been very healthy eaters and we never had any junk food in the house, although I think they have a few takeaways now. I was quite strong on discipline, as was my father, who never allowed us to smoke or drink or anything."
She credits her outdoor life in South Africa for nurturing her own sporting skills, not only running but hockey, swimming, tennis – and Highland dancing.
Brian – who played rugby league at school and in his professional golfing days played in four British Opens, making the cut at Troon in 1983 – says similarly that, when the lads were growing up in Portugal, "we used to pass a rugby ball around on beach and the boys really took to it. And Wellington College was a fantastic school for rugby."
Just 18 months apart in age, the brothers, who share a house (with a rugby nutritionist, Sally will be relieved to know) in Glasgow's West End, are close, although their relationship used to be a volatile one.
"They used to beat hell out of each other," says Brian. "Now the rivalry's still there but they get on better than they've ever done, and I think rugby's done that."
Thom is a fast winger on the field, which his father regards as a maternal legacy, while Max in a recent interview recalled being pursued round the house by his fleet-footed mother: "She had some massive wooden spoons that she'd chase us round the house with." Sally insists that she seldom had to use these instruments of retribution, but kept them in a drawer: "I think the sound of me opening the drawer with some force, and the spoons rattling about, was enough."
Max and Thom are used to facing the limelight outside the rugby ground. Their father is a cousin of Chris Evans, and the ginger-haired presenter has featured the pair on Radio 2's Drivetime programme more than once, while Thom played bass guitar and serenaded crowds of shrieking teenage girls during his stint with Twen2y4Se7en, supporting the likes of Westlife, Peter Andre and McFly.
The Stade de France crowd may be yelling for rather different reasons, but the likely presence of Thom's former bandmates on the terracing may just add, if minimally, to the choruses of Flower of Scotland.