You can use Quiz Scores as a condition for email notifications in Google Forms.
To get started, create a new email notifications and check the "Conditional Notifications" checkbox to configure the conditions.
Here choose Quiz Score from the dropdown and specify the criteria as show here.
Rule #1 - Send email to angus if the student's quiz score is 20 or less
Rule #2 - Send email to kira if quiz score is greater than 20
These conditional rules are part of one email notification rule. If you would like to send separate emails based on different Google Form quiz scores, you need to setup different email notification rules and specify the quiz score criteria in each of the rules.
The No Match Found input box may be kept empty in this case.