Alistair and Jonathan are tipped to do well in the triathlon, but it all evolved from a healthy outdoor lifestyle. The boys were swimmers from a young age. They went through the local swimming schemes near where we lived in Yorkshire, and then to the City of Leeds Swimming Club.

The running started at primary school when Alistair was around nine or ten. I remember taking him to cross-country meets on wintry Saturday mornings.

Cycling was something we did as a family on mountain bikes, and we did a lot on holiday in Spain. My brother-in-law, Simon Hearnshaw, was into triathlon and said there was an opportunity for Alistair to run in the junior national series. He was desperate to enter so we took him down to Nottingham. He was only nine or ten, but he was so determined, and he loved it.

He would do cross-country with the school in the winter, swimming with the City of Leeds or Bradford, and also cycling, which he did socially with friends. Even then, you would cycle with him and he would be off in the distance.

Jonny very much followed in his brother’s footsteps. It was never about myself or Cath [the boys’ mother, a GP like their dad] pushing the boys into it. If anything, we were dragged along by Alistair. He was always very focused. To be honest, we always thought it was a hobby for the boys. They started getting serious about it when they began competing internationally.

Alistair made Britain’s team for the European Junior Championships when he was 14. A couple of years later, Jonny did exactly the same. But we still thought of it as a hobby for them, a pastime. Then in 2006 Alistair won the junior men’s title at the triathlon world championships in Lausanne and a hobby quickly became a profession. He got into Girton College, Cambridge, to study medicine, after pretty much teaching himself further maths at A-level. But it soon became apparent he had an opportunity to pursue a sporting career and it made sense for him to do that now, while he is young.

Alistair and Jonny live and train together in Leeds and are very competitive in the home environment. But they are more supportive of each other while they’re actually competing, which goes against common beliefs about triathlon, which is regarded as an individual sport. It’s a sport that requires a degree of co-operation, and as brothers they have a distinct advantage over the rest. We’re immensely proud of them both. Both boys have done extremely well. As told to Nick Westby

The men's triathlon, taking place in and around Hyde Park, begins at 11:30am on BBC1, BBC Olympics 3

Read our beginner's guide to the Triathlon