Thanks for the suggestions, Gadget. Looking for William Blacker's origins is a direction I hadn't thought of. However, it turns out that he was born in Ireland.
Without knowing where John Fyfe came from, it's difficult to meaningfully narrow down the list of baptisms. However, he declared himself to be Presbyterian on the 1841 Census and his children were baptised in the Presbyterian Church in Carrigallen, Co. Leitrim. John married Margaret Crawford and their children, in birth order, were John, Andrew William, George, Isabella and Samuel, so there was no second daughter.
John Fyfe (Senior) could read and write, a necessity for his position with the Gosford Estates. Was that level of education common among Scottish tenant farmers in the early 1800s, or can it be inferred that he came from a middle-class farming family?
We were talking with our travel agent yesterday. She comes from Elgin (NE Scotland) and said that is a rich farming region and there were Fyfes (or variant spellings) in the area.
We will be visiting Ireland next week and hope to find some more information in the Cavan library.
Dennis