Kia Ora Leonie
I'm also a descendant of this James C Rankin and the Kaikohe Maori woman (Matire Ngapua).
The family has the name Claudian for the middle name of James Rankin. However I was also given the name James Ceerel Cogswell Rankin as well by this Maori woman's daughter.
This James C Rankin was a storekeeper and "legal gentleman" in Kaikohe in August 1894.
Whether he is actually James Caldwell (or Ceerel Bateman) Rankin or not I can't quite determine.
I can trace James Caldwell Rankin's whereabouts to about June 1893 in Auckland. He then reappears in Auckland February 1895 and then disappears and reappears in Australia.
I am interested in information on James Caldwell Rankin in that missing time period of 1893 to 1895. What was his occupation? And what were the birthdays of the two children? That'll help narrow stuff down for me.
And I do have a letter that Elizabeth Rankin nee Bruce wrote to the New South Wales police commissioner in 1900 seeking information about James Caldwell Rankin if you are interested. It doesn't give much more information than probably you already have about him but you might want it.