When searching a Directory by a Student's last name, if you are only seeing two parents instead of four, the other Parents may have a different last name than the Student.
To make sure the Parents are displaying:
Go into > Faculty > Directories > Student
In the Student Directory, search for the Student by last name
Click on Additional Information
This will show you the full names of everyone the student is connected to in the system, including their Parents. If a Parent has a different last name, you can go into the Parent Directory and search by that last name and the Parent should show up in the results.