Hi,
Further update on William Brackenridge, found an article in Scotsman 13 Nov 1880, for him receiving 9 month sentence for forging his father's signature and obtaining a sum of money.
"Wm, Breckenridge (sic) pleaded guilty of forging the signature of his father and obtaining thereby sums of money from Mr Cairns, Union Bank, Gatehouse. He was sentenced to 9 months imprisonment"
Therefore he would be in prison at the census in 1881.
Tom