Thanks to Muggins' most helpful thread on free Scottish resources, I googled "Valuation Roll Glasgow" and found this very helpful site:
http://www.theglasgowstory.com/valsearch.php
In 1901 my great-grandparents with my grandmother and her sisters were living in Robson Street, Glasgow. However, they are not there in 1913.
I remembered I have my grandmother's papers for enrolment in the Women's Army Auxiliary Corps (downloaded from the National Archives) which gives her address as 222 Aitkenhead Road, Glasgow.
I entered the road name, and sure enough my great-grandfather was living there in 1913.
I have always known them by the surname "Johnston", but in 1896 and 1913 they seem to be using the spelling "Johnstone".