Mirsail,
Robert McCormick and Susan were married on 13 July 1874 at Newtownards 1st Presbyterian church. His address at the time was Dalry (Ayrshire) and hers was Cardy.
https://civilrecords.irishgenealogy.ie/churchrecords/civil-search.jsp
Tradition was to marry in the bride’s church, so Susan was probably Presbyterian. So if researching her background I’d focus on those records. The family are Church of Ireland in the 2 censuses so that suggests Robert was of that denomination.
I don’t see Robert and 2 sons Robert & James in the 1901 census. At a guess they might well be away working in Scotland. (That was very common. There were more jobs there and it was cheap and easy to get to).
Robert senior died in 1922. You can view the original death certificate on-line on the GRONI website, using the “search registrations” option:
https://geni.nidirect.gov.uk
You will need to open an account and buy some credits. It costs £2.50 (sterling) to a view a certificate.
Here’s his probate abstract from the PRONI wills site:
Probate of the Will of Robert McCormick late of Cardy County Down Farmer who died 12 March 1922 granted at Belfast to John McCormick and Robert McCormick Farmers Effects £20
The will itself should be in PRONI in paper format.
One of the two Roberts signed the Ulster Covenant in 1912. So that tells you a little about his political views on Irish Home Rule. You can see his signature on this site:
https://apps.proni.gov.uk/ulstercovenant/image.aspx?image=M0023860004
The Valuation Revision records show John McCormick acquiring plot 14c in Cardy in 1871. At that time it was just a house. In 1888, 2 acres of land was added. It remained in his name till 1905 when it changed to Robert McCormick. Also that year Robert acquired 3 acres on plot 14e. 14c & 14e remained in his name till 1916 when he disposed of 14e. In 1923 14c changes to “reps of Robert McCormick” (indicating he had died). Then in 1924 it changes to John and in 1926 to William McCormick. It remains in William’s name till 1929 when that series of records stops.
The property today is up a dead end lane off Cardy Road East, just north of Greyabbey (and very close to Carrowdore). I can’t say whether the McCormick cottage is still standing.
The 1874 marriage certificate tells us that Robert McCormick’s father was John, a weaver. John died at Cardy on 16.2.1898 aged 84. He was married, and there was an inquest. Cause of death was “accidental burns.” I have not been able to identify his wife.
John McCormick married Martha Cooper in Ballycopeland on 8.6.1904. Here is that family in the 1911 census:
http://www.census.nationalarchives.ie/pages/1911/Down/Ballywalter/Ballywalter_Town/265731/
I do not know who the William McCormick was who took over the Cardy property in 1926.