Mema,
Statutory marriage registration started in Ireland in April 1845. Margaret’s & Mary’s years of birth suggest their parents were married before that. In that situation you need to check church records, which are not always on-line.
Tradition was to marry in the bride’s church. Both Margaret & Mary married in Lissan Church of Ireland, so that’s where I’d look for their baptisms and that of any siblings. Lissan’s records start in the 1740s (with a few gaps). They don’t appear to be on-line anywhere but there is a copy in PRONI (the public record office) in Belfast. If you are unable to go yourself, you could employ a researcher. Researchers in the PRONI area: http://sgni.net
Archibald & Ellen’s marriage might also have been in Lissan COI but if she was of another denomination or lived in a different parish then it would probably be there, rather than in Lissan. No easy way to find it other than to search local records in PRONI.
Note Mary’s marriage was in 1862 not 1860:
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1862/09634/5494230.pdf
This may be Archibald in Ballynealmore in the 1831 census. If it is his household consisted of 4 males and 2 females. They were all COI. Ballynealmore (Ballyneill More) is in the parish of Artrea so probably worth checking their records for the marriage and early baptisms.
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Loughinshollen/Artrea/Ballynealmore/12/
It would be easy to assume Archibald had a son and a daughter by 1831 but they may have had relatives living with them. No easy way of knowing who the others were.
