Have just received info from newspaper archives that refer to him as G N Bonar, rather than J N, and that his wife's name was Margaret. Two children (boys) that I know of, but only have their initials R and the other is J. In 1932, these boys are approximately 15 and 14 respectively.
From this, I've done a bit more looking and I found a G N Bonar who was President of the Insurance Institute in Ireland 1926-27, and that he was working at Commercial Union.
If anyone has any information on this family, it would be greatly appreciated.