My knowledge of the family stops with great grandfather James Cowin who I think is the J. Cowin in the passenger list below.He would have been born around 1921.
I will ask some elderly relatives when I get back to NZ in a few weeks and get back to you if anything turns up.

No defined port of entry into NZ
Spray departed Melbourne Dec 1852; incomplete pass list inc. Diggers, J Cowin 31; W Lightband 26; C Gentry 23; J Levick 35; D McCauseland 24; Montague Adams 26; John Young 32; Wm Simmons 27; J Hill 29; W Baker 34; THe last two have no occupations listed.