Schedule Privilege - Private Meetings

Hi, urgent request please -
There are 2 people I have given meeting/calendar 'Schedule Privilege' access to.
However, I have a private meeting coming up soon and want to make sure they cannot see any details of that private meeting. That meeting has been flagged as 'private'.
Is there a way to block their ability to see that meeting at all please?
Note - The pop-up box next to the 'Can manage my private events ' label is not clear or helpful. So I need to know definitively if they can see my private events.
Ideally all meetings marked as private should be totally masked. 
Thanks!