To help you narrow down the death search period, Duncan is still alive in 1871. This entry is from the 1871 index, I think relationships within the household have been transcribed in error but I will leave as is:
Duncan Campbell 66, shoemaker, b. Fort William
Elizabeth Campbell 33, sister in law, b. Aberdeen
Jane Campbell 30, sister, b. Aberdeen
Jessie Campbell 21, sister, b. Aberdeen
Jane A Morrison 5, granddaughter, b. Peterhead
Fanny Stewart 24, daughter, Milliner, b. Peterhead
Ann Frant 21, general servant
Address: 93 Queen St, Aberdeen St Nicholas
Regards.
Monica