How certain are you of some of the dates?
At the moment we have Walter Smith marrying Sarah Ellen Lowe in 1917, with their daughter, Lilian having a son, Eric, in about 1931. Either the 1931 is wrong, or Lilian was born before the 1917 marriage, possibly because Sarah Ellen had been married before.
What about 1986 as a death date for Lilian Stevenson? If that is definite it makes it more likely that Lilian was not born Lilian SMITH.
Do you know the approximate date for Walter and Lilian's marriage?
Richard