Calendar access for different user groups

[LorinPotter]

Searched, but did not find an existing question about this.

Our VB site, www.vulcanriders.us/forum has multiple chapters.

-Need to set up calendars for each chapter, that any guest or registered user can view, but only chapter members may post events.
-Each registered user now had their 'Primary Usergroup' as 'Registered User', with as many as 3 other 'Additional Usergroups'.
-Each chapter's calendar is set up to allow any guest or visitor to view.
-Each member of a chapter should be able to view and post events on that chapter's calendar. But they cannot post an event unless their 'Primary Usergroup' is that chapter's usergroup.

Is it possible, and where, for 'Additional Usergroups' assignment to allow access to posting on caendars?

Right now, a person's 'Primary Usergroup' must be that usergroup to allow posting a calendar event. Since it's projected to have around 1,000 users soon, new users registering and some leaving or moving in and out of chapters, trying just to keep the 'Primary Usergroup' will soon become a full time job.
TIA