One way this can be done is using our add on feature Event Calendar Pro in conjunction with the Feed Manager feature included in mojoPortal.
The feed manager has a setting to enable showing the feed as a calendar, and Event Calendar Pro exposes an RSS feed for each instance of the calendar. So you can setup different instances of Event Calendar Pro on different pages allowing your teams to manage the events in the calendars. Then you copy the feed url for each calendar into the Feed Manager and configure it for calendar display to aggregate the events from all the calendar instances.
You can try this out on our demo site to see if it meets your needs well enough, create a few pages with different calendars and events and then put a Feed Manager on a page and add the feeds from the calendars and set the Feed Manager to display as a calendar.
Hope that helps,