A Post-Script to this thread:
Samuel died 1919 and Mary in 1927 in Ipswich Qld Australia. Samuel's parents were John and Dorothy.
I found Mary's obituary in the local newspaper which was fantastic - it named her parents, date and place of birth, date and place of marriage, the name of they ship that they arrived on, places they had lived in Queensland, stated the name and address of the nephew that she had been living with for the past few years, and confirmed that there were no children, BUT best of all, it stated that her brother William was still living in Morpeth. Excellent news

I had assumed that William had died much earlier because I couldn't find him on the 1881 Census ( I was looking for a man born in Scremerston), now I believe I've found him in Bedlington, with wife and children and his birthplace listed as Tweedmouth. The names of his 3 daughters are consistent with their aunts and cousins, so this is a very strong possibility to investigate.
Sandra