Bob, I found that some NZ birth certificates had the home parish - not just the IOM - of the person who registered the birth, who was usually the mother or the father of the child.
It would be worth buying printouts (photocopies) of the children's NZ birth certs to try to find his parish in the IOM because Christian was such a common name in all parishes.

Also, was any information given at his burial, or on a M.I.? These often differed from death certs.

What date did he arrive in NZ? Did anyone from his family travel with him to NZ or was sponsored by him later?

Sue