Syncing 3 calendars in Outlook

Hello,

I have 3 Exchange calendars in my Outlook profile -

1. Main (hosted Exchange, not O365)
2. 2nd business (hosted, Office365 Enterprise plan)
3. 3rd business (hosted, Office365 Enterprise plan)

I can see all 3 in Outlook in Overlay mode but now I need to publish my free/busy information and looking for a way to get all of my 3 calendar items into one place.

Possible scenarios:

1. Sync calendar #2 and #3 info to the Main calendar (1 way)
2. Sync all 3 calendars onto 4th that I will make available for the aggregated free/busy data (2 way ideally but 1 way will do too).

What won't work:

1. Neither of the 3 Exchange options give me access to Exchange server so installing something on Exchange won't do
2. The couple solutions involving "importing" calendars don't work for my - I need them to stay in sync all the time going forward not just one time snapshot.

Any ideas?

Thanks!

Thank you, Serge B.