The subscription site Roots Ireland has two Bridget Culkin baptismal records in December 1863 and December 1864. Perhaps they died young? There was a James in February 1869 and then another James in February 1883 who I presume is your great-grandfather.
I also located the marriage record onFebruary 12 1863 in Castleconor. With an 1863 marriage, Margaret could not be born in 1851. I did find a Mary 24 1840 baptismal record for a Margaret Howley with father James Howley and mother Bridget Carbine. The townland listed was Doohaney which is actually Dooycaghny in Castleconor civil parish.
Your great-great grandfather James died in November 1902 and your great-grandfather was the informant next to last record
Margaret died in 1916 see sixth record https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_retur...