More questions than answers.....
Do you have parents' names for William and Helen?
Were they married in Scotland? It seems odd that they might have married in Scotland prior to emigrating in 1910 and only have possibly a first child born in 1920. Not impossible, of course, but just seems odd.
Dates of immigration sometimes need to be taken with a grain of salt. The date given may sometimes depend on the way the question is interpreted by the householder. They may have put down the date they arrived at their present address. That being said, I can't find them on a passenger list at the moment, in 1910 or other years.
Anyway, knowing the parents's names, etc. may help.
PB