Sync Issues - Shared Outlook Calendars

I maintain training calendars for multiple instructors.

They "own" their individual calendars and they are shared with me.

The primary source for the events is Microsoft Access. I have a visual basic module in Microsoft Access that runs periodically to update their calendars. So that they have the most current schedule, it deletes everything from their calendar, then adds back the new events.
On the desktop it appears to work as expected. If I run the delete module and go check, the calendars are all cleared out. I run the add module, all the new events are added. Everything looks perfect.

However after a little while, the old events (that I deleted) re-appear so now they have duplicates of everything. My guess is that when I delete things on the desktop, it's not deleting them on the cloud so those events are being synched back down.

If I go in and look at the synchronization properties, it shows 18K items on the server (which is not correct) and 118 items on the offline folder (which is).

On my end, I only see 118 items. On the instructor's end, they see the 18K in duplicates.

What am I doing wrong? Is there a setting somewhere that says which source is the primary? I can I clear the items in the server folder?