Hi Alex,
My line is through William and Elizabeths son Joseph. Joseph would have been my 3x Gt Grandfather. He was born in Longside, and married there too.
As for William and Mary Farquhar, i am still trying very hard to find out more about them. Mary was born 21/11/1762 in Strichen, Aberdeenshire. She and William (senior) had their family in Sileby (not Selby) Leicstershire. I have come across a few possibilities as to what happened to them, but its not definite.
As for the Pickards in Scotland, they farmed in Longside and many other places too. William (1808) is buried in Longside cemetry along with wife Elizabeth. At least 2 other brothers came to Peterhead and lived here.
I have found the grave for Robert Pickard and his family in Peterhead.
If theres anything you want to know then post me a message and i hope i can help you out.