Sharing Calendar with all team members

Hi,
I have 5 Team Leaders... each has 10 Appointment Bookers underneath... the job of Appointment Bookers is to go thru Leads that were assigned to them by their Team Leader and try to book an appointment for the Team Leader thru the Meeting module... the problem is that the Appointment Bookers can't see the Calendar of the Team Leader and their bookings could conflict, i.e. Appointment Bookers might book appointments at the same time.
How can I share one Calendar among all team members so all Appointment Bookers will see one calendar and will not double book?
Thanks

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