Daughter Georgina's name has helped with finding their 1891 entry:
Jane Johnston 48 Farm Servt b. Melrose
Janet Johnston 18 b. Haddington
Georgenia Johnston 4 b. Humbie
Address: 6 Eweford, Dunbar
And for 1881:
Jane Johnstone 30, agr. lab., b. Melrose
Robert Johnstone 9 b. Garvald
Janet Johnstone 6 b. Haddington
Margaret Murray 36, sister laundress b. Earlston, Berwickshire
Address: Humbie
Not much sign of husband Robert Johnston is there
Still can't see how your Jane fits in with this family...unless she didn't like the name of Georgina and changed it to Jane in later years! The daughter Georgina is the only one in the household who come close to anything of what you have for Jane, but all guesses at this stage. You also have the issue of a Greenock birth place that Jane gave in her 1911 entry. Never easy is it!
Monica
