I have a copy of the "Penguin Dictionary of Surnames" first published in 1967...it lists "Isbister as: "L 'estuary/more easterly/outermost farm settlement' ON; four places in Orkney(also found in Shetland), and a typical Orkney and Shetland surname, including that of the first civilian casualty of the Second World War." Bill Groundwater Tucson, AZ