Their day would start with a swim held in the outdoor pool at Frimley Aquatic Centre beside Frimley Park.
The pool is 50m in length, meaning they will do two laps (100m), while 7-year-olds do one lap (50m) and those aged 11 to 15 do four laps (200m).
Next is the bike ride, which goes through Frimley Park's surrounding roads and runs in to the park itself.
This year the siblings would do one lap of the course and seniors (aged 11 to 15) would do two laps.
Of the swimming, running and biking events, both Bella and Brody prefer to bike, and they've had their fair share of bike rides in preparation for the event.
Brody said, due to unfinished road works, this year's cycle course was slightly different, as it would no longer utilise Hawke's Bay Sports Park.
Finally, they would complete a run around the park which is about 1.5km in length.
They were looking forward to finishing the TRYathlon while being cheered on by friends and family, and of course, receiving their medals.
"The best part is reaching the finish line," said Bella.