Sometimes there will be some initial inhibitions and hick ups as people already know one and some of the clever ones will like to show off to others that they are intimate and close. One should not bother for such minor human aggression and instead sternly and strongly focus on one's job.
It would take some time for everything to come to the normal phase and even the clever ones will keep a distance and will not mingle up unnecessarily.
Knowledge is power.
Even in schools also there are many teachers who studied in the same school. But there may be a lot of gap between the year of study and year of appointment. My uncle studied in the school and joined as a teacher in the same school.