I can’t speak to the multiple unit calendars. One caveat that likely carries over from the previous calendar system (if it is possible) is that only someone who has access to both unit calendars would likely be able to do anything with that calendar entry (attendance, crediting to activity logs, etc). It seems likely that the individual would potentially also need permissions to the activity log systems for all of the relevant units, given that the new calendar is (planned to be?) tied into the activity logs.
As far as automatic addition of new invitees, that’s still “in progress”, according to this post a couple of days ago: https://discussions.scouting.org/t/automatic-rsvp-inclusions-for-new-members/381486
For the new calendar, you must first enable RSVP to take attendance, according to this post a few days ago: https://discussions.scouting.org/t/scoutbook-event-attendance/381408/16
