Hello @κΉμν welcome to the Asana Community Forum 
In the project in which you are checking calendar view you have tasks assigned to various team members? Because if you need one calendar to show tasks from various projects then you would have to multihome the tasks to show.
More info about calendars: https://asana.com/guide/help/views/calendar
Currently having multiple assignees per task is not possible yet, however here is an existing feedback request thread for you to leave your vote 
Assign multiple assignees on one task
Can you please clarify exactly what you mean? Whenever a new task is added to a project and assigned this will show in the Asana calendar view as well. More info about the various views https://asana.com/guide/help/views/basics