Shirley,
Your family appear to have lived in a townland generally known as Carrogs (spelling varies). That’s in the RC parish of Clonallon. Civil registration district of Newry. Their parish records only start in 1826 so finding events before that may be challenging.
Statutory registration of births started in Ireland on 1.1.1864, so Margaret’s birth on that date must have been one of the very first births registered in Ireland. I can see 8 siblings after her birth:
Elizabeth 1.3.1866
Catherine 17.5.1867 (probably died as there’s another Catherine later)
Thomas 17.2.1868
Anne 28.8.1869
Catherine 19.1.1872
Rose 13.4.1874
Theresa 24.5.1878
James 13.5.1880
This looks to be James & Margaret in 1911. You’ll note they married c 1880 (which doesn’t seem likely, as they had children born 20 years before that) and they had had 10 children of whom only 4 were still alive in 1911. Since they had 9 children 1864 onwards, that points to 1 pre 1864, who seems to have been Mary bapt 15.9.1861 and so probably they married in 1860. 31 years marriage in the 1911 census is probably a mistake for 51. I don’t see a marriage for them in the RC records for Clonallon or adjacent parishes. Might be worth going through the Clonallon originals on the nli site in case it has been mistranscribed. Be aware that most RC marriages in 1860 and earlier contain little more than the date, the couples names and the 2 witnesses. No parents named etc, so even if you do find the marriage you probably won’t get the previous generations names, which seems to be what you are after.Family in 1911:
http://www.census.nationalarchives.ie/pages/1911/Down/Warrenpoint_Rural/Corrags/259347/
Family in 1901:
http://www.census.nationalarchives.ie/pages/1901/Down/Warrenpoint/Corrogs/1250850/
The house had 4 rooms and 2 windows at the front. Roof was slated or tiled (not thatched) so they were a bit better off than many.
James death in 1911:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1911/05399/4507866.pdf
James appears in the Valuation Revision records as the tenant of plot 15 in Corrags. That was just under 7 acres. (On the modern Lower Carrogs Rd, though the house looks to be long gone now judging by Google Earth). His name is deleted in 1908. Not clear where he went then, possibly to stay with a relative. I can’t immediately see Margaret’s death.
There’s a baptism in Clonallan RC parish records for Margaret Morgan on 20.10.1835 to John Morgan and Bridget Fegan. Sponsors Edward McCoy & Sarah Morgan. Could be your Margaret but without other information difficult to confirm. I'd be cautious about assuming it is your Margaret as I would have expected to have seen a John & Bridget amongst her children, and I don't.
