Great that at least we now know that the marriage you found is probably them??
Someone else suggested that 1852 Derbyshire marriage

(of which I am a little dubious 'cos my initial look at UK census returns, suggested that couple may have still been in England in 1861 ? )
Anyway, as we now have found Mary Ann BROWN (formerley DONNELLY), I think you will probably be able to make more progress in your search, via her.

-----------------------
Mary Ann BROWN - died Wellington 1913The Karori Cemetery record gives her age as 70 years ...
[bc 1843 ]And that is confirmed at BDM (online) with this record.
*1913 / 4544 - BROWN - Mary Ann - 70 years[Date of death deduced from online record is 23 September 1913 ]
[* Just noting there were two Mary Ann BROWN deaths in 1913 - the one aged 76 died in July of that year. ]
-------------------------
~ Lu