I had a question from an Outlook.com user who shares the calendars with other familiar members. When the accounts were on the old server, the calendars were editable in Outlook but aren't on the new server.
The family shares Outlook.com calendar (new server) with each other but in Outlook 2016 I can only view the shared "Outlook Mail" calendars. I cannot add new events to them. They are all read only.
Correct, at this time, the shared calendars are read-only in Outlook. They are editable in Outlook on the web and in Mac (because Mac uses web servers to sync), but not in Outlook on the windows desktop. This is because you can't (currently) assign permissions to the calendars that Outlook can use.