You need two things to be able to perform the above script, the ID of the calendar web part (WPQ12 above) and the XML script to be able to add the required individuals. The way to do this is to follow the following steps:

Step 1: Getting the XML to add the required users

1. Install and start Fiddler
2. Click on the ribbon on the small arrow below “people” then “Add Person or Group”
   
3. This will give you the dialog to select the users, add all required users to be added by default to the Calendar view and then click “Ok” as image below
   
4. See Fiddler log to find an entry to add the users as per the below.
   
5. Then click on the response as text view you will find the Entities string as per the image below.
   
6. Copy this text to be used later in your script.

Step 2: Getting the web part ID

1. Open the page with the calendar web part
2. Open the IE developer tools (F12)
3. Click on the selector arrow and then on the calendar web part (most top level)
4. In the developer tools view you should see Id of the web part as below
   

Step 3: Create the required script file

1. Use the information gathered to construct a JS file as below

1. Save the file as cal.js (any name)

Step 4: Configure the web page

1. Upload the JS file to any accessible location on SharePoint such as the styles library
2. Check it in and publish it if required
3. Edit the page with the calendar web part and add a content editor web part to the bottom of the page
4. Edit the source of the content editor web part and add the following line
   <script src="/sites/<your site name>/Style%20Library/ctrl/cal.js" type="text/javascript"></script>
5. Save the page and then reload it.
6. See the magic happen :)