There is a tool in the description of the group to find duplicates. FormRanger will not update if there are duplicates.
Formranger updates the form based on a time or form trigger. The change happens for the next person to open the form.
If persons A,B, and C open the form at the same time, the form will be updated when any form is submitted. The remaining folks will still see the form as it was when they opened it.
Formranger isn't very useful when the link to the form is shared in a group setting. Sharing the link with the class during the class will cause everyone to see the same form.
Let me know if you have any questions.