Could this be your Robert Stewart in the 1901 Scottish Census?
Robert Stewart, age 21, single, b. Glasgow, foundry labourer, lodger, 243 Parliamentary Rd., St Rollox, Home for Men
Is it possible that some of your Stewarts lived for a time in England? The 1901 Census for England and Wales shows:
William Stewart, age 61, Head, b. Scotland, widower, shipwright, 18 Lowell St, Walton on the hill, Lancashire
Annie Stewart, age 17, b. Scotland, lodger, postal telegraphist, 10 Finlay St, West Darby, Lancashire
Isabella Stewart, age 24, b. Glasgow, housemaid, 4 Egerton Place, Kensington
Elizabeth Stewart, age 18, b. Glasgow, general servant, 45 Lancaster Rd, Carnforth, Lancashire (Her age is out a few years but could have been mistranscribed)
It's a long shot but these census records might be worth a look.
Cheers,
Rodeo