I had a look at the birth indexes and Samuel & Eliza had the following children:
Nancy 11.6.1874 (that’ll be Annie in the 1901 census. Annie & Nancy are the same name).
William 20.12.1876
Samuel 18.10.1879
Alexander 10.12.1882
Ellen 22.1.1887
Maggie 2.7.1889
John 31.1.1892 (Died 1.5.1900 scarlet fever).
George 1.4.1894
Samuel Nugent (born c 1846) died 27.4.1905. His wife Elizabeth died 14.4.1901.
Apart from Alexander & George, I don’t see the rest of the family in the immediate area in the 1911 census. I don’t see them having married in the Kilkeel area 1901 – 1911 and suspect they had left Ireland, presumably after their parents deaths.
The Valuation Revision records show that Alexander acquired the farm from his father Samuel. It was plot 12a in Mullartown, a 6 acre farm. His name remains the occupant till 1920. That farm today is up a dead end lane off the Quarter Rd, near Kribben Cottages.
Alexander Nugent signed the Ulster Covenant in 1912. (That means he opposed Home Rule for Ireland). You can see his signature on the Ulster Covenant site on the PRONI website:
https://www.nidirect.gov.uk/services/search-ulster-covenant
I searched for Mary Hall births in Ireland 1875 to 1885. There are 118. The only 1 in Kilkeel was born 4.12.1874 at Ballymartin,. To William Nugent & Susanna Fitzimmons. William was a farmer. This that family in the 1901 census:
http://www.census.nationalarchives.ie/pages/1901/Down/Ballykeel/Ballymartin/1234484/
And in 1911:
http://www.census.nationalarchives.ie/pages/1911/Down/Ballykeel/Ballymartin/243853/
William had died in 1907. His will should be in PRONI. Here’s the abstract:
Probate of the Will of William Nugent late of Ballymartin County Down Farmer who died 5 November 1907 granted at Belfast to John Nugent Farmer
The only birth in Belfast was Mary Nugent born 4.1.1875 to Peter Nugent a butler, and Sarah Davis. I couldn’t; find them in the 1901 census.
I noted these probate abstracts on the PRONI wills site. Don’t know whether any relate to your family or not:
Nugent, George of Ballyveamore Ballymartin county Down retired fisherman died 12 March 1949 Administration Belfast 17 August to Jane Sloan widow. Effects £230.
Nugent, William of Ballymartin county Down old age pensioner died 6 October 1950 at Ballymartin Newry county Down Administration (limited) Belfast 27 July to Grace Pratt married woman. Effects £526 7s. 1d.