Derek is pre-selected for the 2014 marathon, but his 21-year-old younger brother has designs on the 10,000 metres, despite never having run the distance on the track.
That seems a big ask, but Callum has a prodigious pedigree. He won 14 of 23 under-17 races - including four national titles. Internationals included, he failed to make the podium just four times. The following year, 2009, he won Scottish schools and Scottish national cross country titles; in the summer he took 3000m gold at the European Youth Olympic Festival; and in December he helped Britain to team gold at the European cross country championships. In 2010, he was second British athlete in the UK junior team which were best European finishers at the World cross country championships in Bydgoszcz.
These results brought US scholarship offers, and he was recruited by Darren Gauson, a former Scottish 1500m champion and assistant coach at Butler University, but two seasons in Indiana were blighted by injury and surgery. He is now back home in Kilbarchan, studying mechanics at Paisley University.
Two operations resolved a cartilage problem in his left knee, but even Callum is surprised by recent improvement. "I was running 14:32 for 5k in the summer, then went to altitude for three weeks, came back, and ran 29:40 to win the Glasgow 10k," he says. "That's a big jump in such a short time."
He followed victory at the Great Scottish Run in October with third in the Leeds Abbey Dash last month, and then booked his place in Britain's under-23 team for the European championships in Belgrade next Sunday. He had not raced over the country in two years, and this marks his first UK vest since the World event three years ago.
He was 19th on his European Championship appearance in 2009. "Hopefully, I will do better next weekend," he says. "I'm getting fitter every week, but having been out for so long, I can't put numbers on it. Last year, I had knee surgery in the US at the end of March, but it did not work out, and then another operation back here in Britain, at Christmas.
"The trial for Belgrade was my first cross country in two years, so I was pretty pleased. In the summer I was getting fitter but not quite where I wanted to be. So to come back during the winter and be running as well as I am now is quite nice.
"The cartilage problem happened in my first year at Butler, but I just ran on it, because it simply felt like a niggle during the indoor season. It went away during the summer and didn't come back until the next year. We're not sure what caused it. I fell in my first winter, and hit a rock, right where the cartilage tore."
Basketball is king at Butler. Their 10,000-capacity hall has a 240-metre indoor track running high above the floor. "A kind of balcony, barely one-and-a-half people wide," says Callum. When ice storms drive the athletes inside, it's a suitable refuge.
"Often we trained outside in minus-10. Yet I find it harder to get motivated at home, because it's darker longer. Coming back, I felt I hadn't seen the light all winter. It was quite depressing.
"My first US cross country season wasn't the best, but I got it together for track, and made it to the regionals and ran a pb for 5k. My second cross country season went really well. I made nationals, and went all-American, and finished 22nd in the nationals. The team was really good, with a good atmosphere. I'd Darren's brother, Kris [another former Scotland 1500m champion] for company in my first year, but with the injuries, I was happy to come back.
"I have restarted my degree at Paisley. I was a bit stupid, that first year at Butler, mucked about a bit. It was a harsh lesson."
As European Youth Olympic 1500m champion, one might suggest his breakthrough came too easily. "I don't think so. I had a down year after that. I was only about 90% of what I should have been, but in my second year at uni, I was probably running the best I ever had, but the knee injury postponed me for another three years."
The 2014 Games have been a target since he was a 15-year-old pupil at Gryffe High School - the day he heard Glasgow would be the host city, back in 2007. "My pals - and my maths teacher, I think - asked if I'd be running there, and I said: 'Yes'. So it's always been a goal - but not the 10k. That's only since the surgery.
"I was aiming for the 5000, but I'd need to do the qualifying standard twice, whereas I only need the 10k once. So I'm hoping to do a 10k at Stanford at the beginning of April.
"I need to find 26 seconds [from his best road performance]. I haven't run 10k on the track. I was supposed to do one just after I got injured. I am not even up to full mileage, and my sessions are not quite at full distance, so I'm quite confident that if everything goes right, I should be able to run the time."
He is indebted for the support of his family and sponsorship from Renfrewshire Council and the AM Ross Foundation. And he says it has helped, rather than hindered, having a family steeped in the sport. His brother, Derek, won Scottish cross country titles in 2009, '11 and '12, and was first UK finisher in the London Marathon this year. His next major goal is the 2016 Olympics.
Another brother, Scott, was a Scottish age-group champion at 1500m, while their father, Robert, who has coached all of them, won the Scottish senior boys' cross country title 34 years ago.
"I wouldn't say that put pressure on me," says Callum. "In fact, it maybe helped me get out the door - stopped me being lazy. Having my brother run so well, there's a bit of rivalry, trying to out-do each other."
He and Derek train together when they can, but avoid steady runs. "We'd just end in a burn-up, racing each other, but we do things like 10 x one kilometre, or 5 x a mile, together. We help each other, but we're always teasing and winding each other up.
"If I can make the Games team it would be pretty special after the last couple of years. It would mean I was back, and it would be quite something to have two brothers in the team."
The last brothers in a Games athletics squad was in 1970, when Ian and Peter Stewart were first in the 5000m and fourth in the 1500m, respectively. He was unaware of this but said: "That would be a really good piece of history to match."