"It's a little village school that's had nothing, but through our visits and financial support, we've managed to build a strong network and helped kids top the league tables with their school results," said Bethlehem principal Eoin Crosbie.
The group left New Zealand on December 28 for a four-week volunteer project building classrooms for the impoverished school.
They were just days away from returning home.
The tragedy has left their families and the Bethlehem school community in mourning.
College principal Eoin Crosbie said the Johnstons will both be remembered today as a one-of-a-kind couple.
He says the family has a long a close association with the college.
The Johnstons, who had 10 children, were heavily involved in the college and would attend most school events or functions. "Even if their children weren't in them, they would still go along to support the others", Mr Crosbie said.
All 10 of their children attended Bethlehem College, where two are still students.
The funeral for the third member of the group killed in the accident, 19-year-old Caitlin Dickson, was held on Thursday.