She described her late sister as having been fit, strong and healthy.
Bristowe is survived by three sons; Robert-Daymond, 11, Ruaumoko, 10, and Rongomaiariki, 2.
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It was heartbreaking to see them after the tragic loss, particularly the youngest, Engels said.
"He is so attached to his father at the moment, I guess he senses that something is amiss.
"His mummy is just not around and she is the main caregiver for these kids."
Her eldest son had a heart arrhythmia and had already survived two major surgeries, with an unwavering mum at his bedside.
"She wasn't unknown to the surgeons or the hospital - just not for her.
"To our knowledge she had no heart problems."
All of the siblings had been checked after their father, who had a heart arrhythmia, died.
Bristowe always made sure her children received the best medical care and had every appointment well documented in her phone with a reminder.
She was also a keen sportswoman having gained a black belt in martial arts while growing up in Wellington. She would later move to Auckland before moving to Melbourne.
There Bristowe played a huge role at the St Kilda City Football Netball Club.
She had been recently made a life member, Engels said.
"This is a woman who umpires, coaches, teaches, picks up and drops off, she's sitting there behind the tuck shop, organising trials, uniforms, fundraising, bringing kids along..."
Her keen community involvement was reflected in the huge outpouring of love towards the family following her death.
"They are holding us up," Engels said.
It is with deep saddness that we inform you of the sudden passing of Tui who passed away in the late hours on Saturday...
Posted by St Kilda City Football Netball Club on Sunday, 26 January 2020
People had been showing up in tears with bags of shopping to gift to them.
"Just to make sure we would never have to want for anything.
"It's a little tough for them because I look very similar to her."
The siblings had enjoyed a classic sisterly bond growing up and as adults Bristowe had always made time to take calls from Engels who is based in Amsterdam.
"She let you know you were special," she said.
"It is heartbreaking because she made me feel like I was the only one that existed and she did that for hundreds of people.
"When you called you she was always like: 'hey come over I'll make you something to eat'."
When Engels got the call that there was a problem she had immediately got on a flight to Australia.
But she learned she was too late during a stopover in Indonesia.
Bristowe's partner Gordon Mako will now have to raise the boys as a solo-dad, so Engels was asking for financial assistance to help the young family.
Bristowe's body will be repatriated to Auckland.