So many people helped me out during my trip: librarians, history buffs, B&B owners. Yesterday, I came home to a package from Ireland. What could it be? I wasn't expecting anything. It was from the National Archives in Dublin. I opened it up, and inside were the copies of wills from the Holmes family. I thought I had them with me; I hadn't even missed them, yet. Some very thoughtful employee at the Archives had simply mailed them to me, internationally.
Last night I drew out the family relationships from the wills. Their Mary Holmes is too old to be my Mary - she was old enough to be an executrix in 1691, whereas my Mary was a newlywed in 1725, who had several children after that date.
I still think the family is connected. They have all the right family names. Several wills mention only "the younger children." Mary could still be a granddaughter of Peter and Bridget Holmes. Richard and Isabell Holmes are the right ages and the right county to have been at Mary's wedding. Richard could be Mary's older brother, but my guess would be a cousin.