Since leaving Los Angeles in July the brothers have travelled through Canada, Mexico, Barbados, Costa Rica, Ecuador, Brazil, Iceland and Kazakhstan and visited Edinburgh, London and Istanbul.
They will be paid $50,000 by the internet travel company when the adventure to 25 destinations is completed.
The 12-day New Zealand leg of the world tour will be showcased as a "must-visit" tourist destination using blogs, videos, articles, social media posts and interviews.
The chance to come to New Zealand to find their roots was an amazing opportunity, they said. Their great-great-great grandfather, Nathaniel Ayling, arrived in Invercargill in 1875 with eight children after a 144-day ship voyage from London, and losing his wife Mary Mann to sickness en route.
"We're just so excited to be coming to New Zealand, a country that we have a strong connection with," Alex said.
"We won the competition in London and just like our ancestors did, our journey from London will be complete when we reach New Zealand."
My Destination managing director Mike Watt said it was a privilege the brothers chose New Zealand as the final destination.
To follow the brothers' worldwide journey go to www.mydestination.com/bbb, www.youtube.com/watchbbbtv, or Twitter #MyBBB.