Hi Colette!
I'm assuming this family was Roman Catholic?
The baptismal records for the combined parish of Aglish(Castlebar), Breaffy and Ballyhean do not start until 1838. Marriages start in 1824.
I searched the subscription site and could not find a marriage record for Edward Gordon and Mary Reid or any Mary.
I also did not find a baptismal record for younger siblings of William.
Roger McDonnell