The only information I have is that William Moffat married Helen Oliver - there are no dates of birth, no marriage date and no location data. It is possible William was a soldier, as indicated below.
The 1901 Scotland Census shows a Helen Moffat with six children residing at 43 Beckford Street in Hamilton, Lanarkshire, Scotland. This address now looks to be within the bounds of the University of West Scotland. Helen was then 40 years old and was born in Glasgow, therefore, in about 1861. Her husband was obviously not at home at the time of the census and she records she is a "soldier's wife".
The children mentioned in the census are:
This could well be the family of Margaret Hamilton Moffat then aged 14. The year of birth fits with what we know already, as does the fact that we believe she was born in England, although I thought the sister called "Jane" should probably have been called "Jean". Maybe it is a typo in the Ancestry.com transcription of the original record.
There is a note in a small incomplete diary kept by James Wilton (b 1885) that refers to a Dr N or W Moffat in Ireland. I assume the reference is to his father-in-law, William Moffat.
The photographic record is both slim and unclear. The photo above is, I believe, to be of Helen Oliver, but I am by no means certain that it is her. The photo of Nell (Helen) is, I believe, properly identified.
Is it sheer coincidence that in 1901 they may have been living in Hamilton and that the first born, Margaret, has Hamilton as her middle name?