During import, students and guardians are combined into families in a couple of different ways. Our first attempt at creating a family is done using the address, so if two students have the same address, they are considered to be the same "family". If there is no address listed for the student, then we will attempt to find another student with the same home phone number.
If neither of these fields are contained in the data or found for a particular student, then we use the guardian name with at least one other identifier (email or phone number). If no match can be found on any of this to another line on the template, a new family is created.
If you find that two students who are in the same family were not grouped together, simply add the student to one of the families and then delete the other family.