my activities appear in all colleagues calendar

my activities appear in all colleagues calendar

Hello,
I have professional use of ZOHO CRM and I also have 2 colleagues using this tool. We took this professional use because we wanted to use the calendar sync of zoho calendar to google calendar. It does work, however if one of us (3 persons) put an new activity it appears in all our google calendar and not only in the one who created it. Does anyone know how to sikve this?
Many thanks in advance!