The welcome email a person gets when you run the "Send VC Welcome Email" Action menu item is determined by that person's security role.
In Veracross, there is an important distinction between a person role and a security role. Someone who has the person role of Parent of Prospect will automatically be assigned the corresponding security role of Parent of Applicant in the overnights. Knowing this, you can then review your school's Security Roles query on the System homepage to determine which VC Welcome Email template is configured to be sent to people with the security role of Parent of Applicant. You can update which template is associated with each Portal Role directly from this query.