I think that this is about as far as I can go with your family. I have looked through the 1851 census and extracted those entries for unmarried William Roberts' that appear to fit in age and birthplace.
HO107/2172/46/256
Chester St Peter
Address Watergate St
William Roberts, lodger, unm, 18, Ostler, born Shropshire
HO 107/1990/12/164
Shropshire
Condover Village
William Roberts, servant, unm, 18, Farm Labourer, born Salop Condover
(living in the household of Thomas Bower, Maltster and farmer of 26 acres, employing 1 labourer) - presumably William Roberts
HO 107/1992/260/3
Shrewsbury St Mary
Address - Castle Foregate
William Roberts, serv, unm, 17, house servant, born Salop Shrewsbury
(in the household of Frederick Hammonds - Fishmonger)
HO107/1994/445/1
Great Ness Shropshire
William Roberts, serv, unm, 19, B, Smith, born Salop Shropshire
(living in the household of Richard Blacksmith employing 1 man)
(in the same household there are:
John Jones, Apprentice, unm, 17, B Smith, born Salop Shrewsbury
Martha Jones, servant, unm, 13, born Salop Shrewsbury)
Good luck with your searching
Nell