Hi Marengo,
you mention he was known as George Nash only but all the records I can find on him he is Richard George Nash.
Marriage;
Richard George NASH
Emma CULL
1875/1101
These children all have their Father recorded as Richard George Nash on their birth regos plus Mother Emma.
Annie Jane 1878
Caleb John 1880
Emma 1881
Charles 1885#
Samuel Corea 1886#
James 1888#
(# ones you have mentioned)
Trish 
I'm not sure how old this post is but I have just read thru the posts here and would like to state that Richard George Nash was my Father's Great Grandfather and an artist in Invercargill, New Zealand. We still have several paintings in our family that he did.
I hope this helps in some way for your search.
best wishes
Roniece