According to the 1881 British Census a William Conwell,widower,age 77,formerly Agricultural Labourer,Grandfather,born Isle of Man was living at Apsley Buildings,Wavertree,Lancashire with James Conwell Age 29,Head of Household,Occupation Civil Service Messenger (Letter Carrier)Born Isle of Man,Wife Sarah ,Age 26,Born Isle of Man and two children Elizabeth M. age 2 and William J. age 1 both born in Wavertree.
Wavertree is a suburb of Liverpool.
He may be your William living with son James and family.