The Death notices for John and Carrie are no help re William.
It's not the one who died in 1948. There is no Death notice for the one who died in 1936. Can't find a notice for the one who died in 1935.
1920, 1922 & 1924
GUY Robert F, Colin st, Lakemba
Birth 31257/1895 GUY WILLIAM H - WILLIAM H - CATHERINE - CANTERBURY
GUY W., Dunstaffenage st, Hurl. Park
1920 & 1922
GUY William, Fore st, Canterbury
1922 & 1924
GUY William T., 11 Hargrove/Hargrave st