Plain text agenda formatting recognition by Siri
I do not really understand why Siri should be involved?
First create a new calendar (click on the “File” menu, select “New Calendar” and then “iCloud”). You can name it to whatever you feel like and share it by clicking share icon to the right of the calendar’s name. You can even make it a public calendar, which means anyone can subscribe to a read-only version of your calendar.
Second define all events in this calendar. (For future changes make sure to have syncing of calendars to iCloud activated).
In the edit screen of the calendar you can directly add people with whom you want to share it.
Apple provides more info here.