You could add the article the front desk teachers. I assume it has been omitted for the sake of brevity. If the lesson/lecture is over , the past tense (were) seems logical.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
nikoer30127"Inform the desk teachers if there are any absentees."This is fine when said before the lesson. The past tense is fine if the lesson is over.