It is difficult to see what became of the family after 1871 census.

Yes, I agree, we really need to hear back from stewart-r.
I wonder if this is William in 1881 census Gilmour street, Edinburgh, St Cuthberts
William Stewart 34 Head, Tailor, born Edinburgh
Catherine Dall Or Stewart 28 Wife, former servant, born Glasgow
William Stewart 2 Son, born Edinburgh
William Stevenson 12 Nephew, born EdinburghRobt Stewart Stevenson 9 Nephew, born Edinburgh
It does not seem right with the other nephew, and age not quite correct.