Hi Jenn and Trish,
John disappears from Scottish records after the birth of his last child with Ann in 1869. Ann calls herself a widow on the 1871 census, and dies in Barnhill Poorhouse in 1872.
So I'm guessing John left sometime after 1869. On the IGL there is a child birth,1874, in New Zealand, the John who dies with his brother in Dec 1885. The other children's births are listed on the NSW register.
I'm thinking John might have been a convict, but would he have been sent to NZ? Or maybe the IGL is wrong about little John's birthplace.
I'm hoping someone might offer to look up the details when they visit the NSW registry, or if this is this not an option, I'll get the transcription service to do it.