Thanks for the replies minniehaha and althea,
Yes the other child born to Hannah and Hugh is definatley mine (she is my Great Grandmother) she was born in Westport (according to her marrige cert) and I think it would definatley be worth having at look at what the guide book says as there is what looks like a question mark after that entry of "Birthplace" on the cert.
Hugh was a baker and a missionary (new piece of info to me) and seemed to live all over........Otago, New Plymouth, Bay of Islands, Westport and Wanganui. These are the ones I know about)
Hugh and Hannah married in Westport on 8th Oct 1868, so dates for a birth would fit

I have looked at the Dunedin cemetery site and there are a lot of "NEIL's" buried there, but seems a bit odd another couple being Hugh and Hannah. (I am doing a lot of checking as I got caught with something very similar that happened last year, but the names were a bit more common)
On both Hugh and Hannah's death certs it dosn't state a living male, only daughter Frances is mentioned (and Hugh's daughters from his first marriage) (Scotland)
Thanks for everyones input, I am off to have a look at BDM am having an idea (will report back on my theory)
Gail