The pair, aged 32 and 31, had been travelling through the Baja Coast region with their friend Jack Carter Rhoad when they disappeared on April 27.
A search was launched but the men were found at the bottom of a well weeks later and three Mexican locals were arrested.
Authorities are investigating how the brothers died , while friends and family reflect on how they lived.
Hundreds of people gathered at Sacred Heart College in Sorrento yesterday, where the brothers had spent their high school years.
Their parents, Debra and Martin Robinson, reflected on their sons' "beautiful lives" at the memorial service.
"Callum and Jake meant so much to us and it's still hard to imagine life without them," Debra said.
"They were intelligent, respectful men and they had so much more to offer the world.
"They loved life and they followed their dreams."
Family and close friends of the brothers recalled fond memories of the pair, who shared a love for people and adventure.
"We're not here to dwell on the where or the how or try to understand the why of their passing but instead to say goodbye to two young men and hopefully start the healing process," Martin said.
Callum was remembered as a force of nature, known as the big koala to his American friends, and a professional lacrosse player who did things his own way.
"We miss your bear hugs, your trademark smile and your infectious laugh," friend Adam Moore said.
Jake was remembered as a young doctor on a mission to help others.
"Walking alone between venues in North Bridge when he came across a man who had overdosed, rather than worrying about his own safety and walking past as many others did, he stopped and administered first aid until the paramedics arrived, effectively saving the man's life," friend Ruairy Read said.
"We're so grateful for the profound impact that Callum and Jake continue to have on our lives in such a positive way," friend Simon Moore said.
"We will for ever treasure and share the memories of the boys for the rest of our days," Adam Moore said.
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