Through some good fortune, over 55 New Zealand (and some in Australia) relatives were added to the family tree in 2005.
The first that we can track Isaacs – Myer Samuel Isaacs – moved with his family from Holland to London in 1814 to escape the Napoleonic wars. Three of his sons became prominent rabbis and spread around the world:
David Myer Isaacs practiced in England
Samuel Myer Isaacs went to North America (New York)
Jacob Myer Isaacs traveled to Australia
It is the descendants of Jacob Myer Isaacs who have been added to the family tree, including Daisy Isaacs who lived to the ripe old age of 100 when she died in 1986, and her brother, David Nathan Isaacs, who served with distinction in World War I and lived "only" to age 96, down to the youngest 7th generation daughter named Helen Louise Cooke, born in 2003. All lived or live in New Zealand.
According to Mary Watson of Auckland, New Zealand, writing in 2010, the first Isaacs emigrated to New Zealand as follows.
Rebecca Isaacs (born Sydney 1841) returned to London with her family in 1857 and is found in the United Kingdom Census of 1861. She came to New Zealand on the Indian Empire which arrived in Auckland Oct 20, 1862. Gabriel Lewis took out an "intention to marry" notice on 24 Mar 1863 and they married May 19 1863 at Beth El Synagogue Auckland. Gabriel had arrived in the colony on 25 Feb 1856. Of course, he could have met her in London (or even Sydney), but Mary Watson has no evidence he left New Zealand in that period. However, it was always extremely hard to find suitable Jewish marriage partners in the country Most single women (of any religion) came to NZ at that time for one of four reasons: to join family already there, to be married, to be a domestic servant/governess, or to be a prostitute.
Nathaniel John Isaacs came to New Zealand in about 1868. He was employed for some years as a commercial traveller for Lewis Bros, settling in Wellington in 1876 as an auctioneer. The chain may have worked as follows. Edward Lewis arrived 6 Sep 1855, and Henry possibly in the same year (he claimed he was in Sydney in 1854). Gabriel and Michael came on the same ship in 1856. One of their sisters, Matilda Lewis, appears in the United Kingdom Census in 1861, arrived in Auckland in 1865 and was married there 13 November 1867 (clearly not an arranged marriage). A descendent of Matilda is adamant that Gabriel was the instigator of the chain - hard to believe looking at the dates. At any rate, Mary Watson guesses that Rebecca encouraged Nathaniel John's emigration and found him work in her husband's business. Quite a miracle as Lewis Bros went bust twice between 1867 and 1878. This was a common fate as the colony struggled mightily to find a raison d'etre.
I welcome any updated and additional information.