William had a brother John born abt 1831 in Comber, Newtonards, Co. Down, Ireland and died Nov 1, 1899 in New Luce, Wigtownshire, Scotland. Perhaps if he has an obituary or writeup, William might be mentioned.
William also had a sister Jane McMaster Scott nee Johnston who died Feb 26, 1872 in the Parish of Stoneykirk, Wigtownshire. Perhaps her obituary or write up would mention her brother William and/or his whereabouts.