Their sons can now take solace knowing the search for their parents, who went missing in last month's deadly earthquake in Nepal, likely saved others.
"It helped a lot with knowing that, yeah," said their son, Fraser Macmillan, 28. "We had this loss but maybe other people survived for it, for us doing this."
Fraser, and his older brother, Jay, returned from New Delhi last week after a desperate search for their parents. They were on a hike in Langtang National Park on April 25 when an earthquake triggered an avalanche that wiped out villages, blocked roads and cut off communications.
While there is no official word, the Macmillan brothers, who worked with family in Canada to compile a database of information, said they have pinpointed their parent's last location, and all evidence indicates they did not survive.
There was a 20-kilometre zone of massive destruction, they say, where more than 4,500 people died. Only 12 survivors emerged from that area.
One woman they tracked down met Kathy and Bruce just before the disaster. She made it out of that danger zone and waited for the Macmillans to follow, but they never did.
When the brothers heard that - they knew.
'The soul tells you'
"The soul tells you," said Jay, who along with his brother is now sharing their family's story for the first time since they confirmed their parents' deaths. "We had enough evidence to know it was time to start healing.
"It was kind of like a bittersweet emotion. It was like a deep, deep hug and a deep, deep cry, and like a little bit of a relief the nightmare had ended for us."
It began as a family adventure. Kathy, a retired nurse, and Bruce, a retired forester were traveling in Asia. The close-knit family were supposed to meet up in Nepal for a three-week hike. Instead, the earthquake forced Jay to stay in New Delhi and trapped Fraser in Kathmandu, where he slept in a field for two nights, then took refuge on a U.S. military compound.
Fraser said it put him in the perfect position to relay detailed information to search-and-rescue teams arriving in Kathmandu, including the GPS co-ordinates of survivors.
"To know we had a part in that means a lot." said Jay. "You could really sense a lot of love in the people who were looking. And they were doing the same thing for us.
'Hundreds of heroes'
"There are so many threads of heroes. It was any moment of the day a shred of information, any story, anything. And there were hundreds and hundreds and hundreds of heroes."
On Saturday, the family broke their tragic news to a network of supporters worldwide - many of whom had joined the Facebook page "Find Bruce and Kathy Macmillan."
The page quickly swelled with messages from hundreds of people whose lives had been touched by Kathy and Bruce - whether they knew them or not.
Many noted their kindness, sense of humour, wisdom and spirit, which now lives on in their sons.
"That's why we were in Nepal and in India when they passed on," said Fraser.
"We were following after them, because their path was just - it seemed like the way to live. You could see through them that they're happy and it's just like, 'Oh wow, that's a good way to live.' "
'A really cool guy'
The brothers say they their parents taught them about love and joy, about doing things they enjoyed, about not wasting time, about how to avoid all the petty stuff. Their dad, Fraser said, "was just a really cool guy."
Jay talked about his mom's contagious laughter, the way she would be in stitches and soon everyone was splitting a gut.
He said his mom spent most of her life making sure everyone else was OK. "That's what makes me really sad. Now she was really living for herself. And they had a lot of good years ahead of them. It was going to be fun, hanging out with them."
The Macmillan brothers vow to carry on the legacy their parents left them, through their acts of compassion, their sense of adventure, by not shying away from the mountains, by going to the places where you learn the most.
"You can see it in all the photos," Jay said. "You can see it in their faces. When you look into their eyes, you can see a contentment there. Contentment is the closest thing to enlightenment. And when you're enlightened, you have the choice to leave this world and go to the next, and that's the peace we take with us. That they were content."