Hi Sue,
Thank you for your thoughts and all the information regarding possibilities. I think that the next thing I can follow up is the farm and when he purchased it (or if it was a land grant when he obtained it). I know exactly where it is as my Mum remembers visiting and the nearest town (Mangatainoka). Perhaps "Maryalias" is the name of the property and maybe it still exists.
Anyway if I can find when he obtained the property it will narrow down when he arrived in NZ a bit better.
My mum says they (the brothers) travelled to NZ together and then, after some time, the brother went on to live in Australia.
I will also apply for the remaining paper I do not have from NZ (their marriage certificate & his death certificate).
These things can take a while so perhaps I should get these before chasing around the IOM again?
Best Regards & thanks to everyone
John