score:3
No one can predict the outcome, but best practices would indicate that an absolutely fresh application should be made. This is to avoid two important considerations:
Previous names are an important data item, and clicking "yes" opens up a sub-menu. Accordingly, a simple pen and ink correction to say "yes" will not suffice.
Yes, again best practice; cancel the application and say it had a mistake, not a big deal.
And you do not need to cancel your son's application. You can change the GWF in the remarks section with a simple pen and ink correction.
Best practices prevail when there are no explicit rules, and generally reflect what you could expect to hear from an experienced lawyer.