They were working up to 16 hours a day and sleeping remotely in tents.
Temperatures are 30C-plus during the day but plummet to about 6C at night. The firefighters' contract has been extended for another two weeks and the brothers are expected to fly back to New Zealand on September 12.
"The experience they've gained will bode well for them in future and it will also help Forest Protection in its work," father Mike Sullivan said.
He said the rest of the Northland crew were mopping up, creating fire breaks, and patrolling areas where flare-ups could occur at Elephant Hill.
Work is quite intense, he said, with a lot of hose lines to carry and patrols for long hours.
Forest Protection Services' owner Kevin Ihaka is also helping out but in a supervisory role.
Mr Ihaka said crews have just finished their first stint in the West Chillcoltin complex where fires in mountainous country have resulted in many communities being evacuated.
"There are a lot of fires in the region so resources are pretty stretched and many of the Canadians have been working in very tough conditions for a long time so they are grateful that we have come to help.
"It may be many weeks yet before it snows here and finally ends the fire season. While we have worked on fires this size before I don't think we have had the number of fires at once before," he said.
More than 400 firefighters from Australia, New Zealand, Mexico and the US will arrive in British Columbia over the next week to fight the blazes. They will be a mix of specialised support staff and highly trained and experienced wild land firefighting crews.