Paris Paralympic Games: Twin para-triathletes aiming for glory
For most siblings, their sporting rivalry never goes further than the back yard of their childhood home or lasts beyond their teenage years.
But 28-year-old twins Chloe and Judith MacCombe have taken theirs to the top level.
The Northern Ireland para-triathletes are hoping the competitive edge they share can push them towards Paralympic Games glory in 2024.
The sisters have a form of albinism which affects their vision.
They took up triathlon just over four years ago and compete in the PTVI (vision impairment) category with their guides.
Chloe and Judith, from Claudy in the north-west, recently received a £1,000 bursary from the sports charity The Mary Peters Trust, in partnership with Hughes Insurance, to help them on their journey to the games in Paris.
Speaking to BBC News NI, the sisters say they first got into the sport by accident.
"We were involved with the development programme for the para-rowing team for Ireland," says Chloe.
"That fell through and we just so happened to meet somebody from Triathlon Ireland and they asked: 'Can you swim? Can you cycle? Can you run?'
"We attended a training day in Belfast then the next month and it just all started from there."
'We drive each other on to be better'
The twins say they could just about make it from one end of the pool to the other at the start but fast-forward four years and they are now competing against the best in the world.
Triathlon is one of the most physically-intense competitions, requiring training in cycling, running and open-water swimming.
They believe their sibling rivalry has helped to push them on in what is a gruelling sport.
"That's how we have managed to get to the level we're at so quickly," says Chloe.
"We do support each other fully in races we aren't competing against each other.
"In races when we are competing against each other, well it can be a little bit difficult - it can be tough if Judith wins and I'm a few places behind her but we always try to drive each other on to be better."
The pair competed in the Commonwealth Games in Birmingham last year and say it was a surreal experience.
Chloe put in a blistering performance to claim a sensational silver medal in the women's PTVI alongside guide Catherine Sands, while Judith narrowly missed out on the podium, finishing in fourth place.
Chloe's silver medal was Northern Ireland's second prize of the Birmingham Games.
Now the sisters are seeking qualification for the 2024 Paralympic Games in Paris and will need to amass as many points as possible from their remaining qualifying races to get there.
But competing in high-level sport comes with many financial costs, and Chloe says that many athletes like themselves would not be able to compete without assistance.
The Mary Peters Trust was established to create a meaningful commemoration of Lady Mary Peter's historic gold medal win in the 1972 Munich Olympic Games.
Lady Mary says it has supported more than 4,000 athletes in Northern Ireland to pursue their sporting passions.
She told BBC News NI that money should never be a barrier for anyone wanting to get involved in and enjoy sport at any level.
"It's so expensive now for everything - the tandem bikes that Chloe and Judith both use for competition can cost more than £10,000," said Lady Mary.
"You also have all the expenses involved with training and travelling as well - Judith is just back from Mauritius for a competition there so it all adds up."