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I searched on two subscription sites, Roots Ireland and Find My Past and did not locate the marriage record for James and Margaret. If they were RC then the church marriage record would not show the names of the parents of the bride and groom. If the marriage was non-RC then the marriage should have been civilly recorded and would show the names of the fathers of James and Margaret. As I indicated, I did not find a record.
You may want to add the emigration story of James and Margaret to our XO Chronicles site and possibly someone will see a connection https://www.irelandxo.com/ireland-xo/history-and-genealogy/ancestor-data...
Have you considered DNA testing?