There are a large number of families with the surname "Sneddon" in Bo'ness. Also Grants (my family) and Hamiltons. My cousin, Archie Grant, has been researching our family tree for many years and has often been on the wrong track because of this common surname thing. It doesn't help that they name the children after their parents and grandparents either! Most families have a nickname they're known by, which doesn't really help with the research either. This hasn't really answered your question of which family you should be looking at. You could go to Scotlands People and try to figure out which of the two couples are your Euphemia Snaddon's parents by finding Euphemia's birth in the Parish Register.
Cheers
Diana