I have a faint glimmer of hope with my Mary Campbell - surely that family has to keep me in Scotland. I will start a new thread about her later.
If I may be so bold, there are two reasons for not starting a new thread.
First, if you start a new thread, then people who have not read this thread may not realise that all this information has already been found, and they may duplicate what has already been done.
Second, if you start a new thread, then those who have contributed to it will not be notified of your futher enquiries about this family.
I venture to suggest that you should just carry on this thead, but I've altered the title to 'Samuel Hendrie and Mary Campbell'.
Have you got Mary's death certificate?
1861 census index has in
District 639 (Dalziel), ED3, page 4 Samuel Henry, 24, born Ireland; Mary Henry, 26, born Ireland: John Henry, 2, born Ireland.
District 652.2 (Old Monkland), ED 13, page 13 Samuel Hendry, 35, born Ireland; Mary Hendry, 31, born Ireland; Elizabeth, 11, born Ireland; John, 8, born Ireland, Margaret, 6, born Old Kilpatrick; Jane, 2, born Ireland.
Neither of these matches your Samuel and Mary's family, however, who were Mary, 1857; Samuel, 1857; and William, 1867. Unless it's the second family, and their daughter Mary had died, and they'd been back in Ireland for long enough for Jane to be born there in 1858/9.