Meanwhile, Otamatea College's Simon Parker will line up in the loose for the Barbarians after impressing at a development camp at Massey University's Sport and Rugby Institute in Palmerston North.
Coach Brad Mooar said his team had an exciting mix of players with the potential to produce exciting rugby.
"It's a talented group that has a good mix of power, size and skill. We want to see them express themselves on the field and represent the Barbarians Club with pride."
The New Zealand Schools Barbarians team will remain in camp in Palmerston North ahead of their first match tomorrow against Tonga Schools. The Schools Barbarians face the Maori Under-18 side on Monday.
Reihana and Williams, like the two Northland Under-18 Maori players, are completing their studies in Auckland but grew up in the region.
Reihana and Williams also go to St Kentigern and play first five and prop respectively.
Coach Jason Holland said there were tough decisions to make in selecting the New Zealand Schools team for their trip to Australia.
"The camp has been very high quality and the players have really applied themselves over the past few days," said Holland.
"The guys have come to us in good nick and we've got a squad with strength and depth across all positions."
The team were due to depart for Sydney yesterday. The New Zealand Schools side face Fiji Schools tomorrow, Australian Schools Barbarians on Monday and Australian Schools on October 7