Part of your problem is that your attributes are not fully mapped from the second entity to the calendar. You have ID set as Mandatory in your entity, but are not passing an ID to the Calendar. If it were me, I would have both refresh actions run, append the results to a growing list, and then iterate through the list to attach the activities to the corresponding day. 

If you use the AddEvent client action, you can loop through as many different lists as you'd like and add the items one at a time. Otherwise, you could try to merge your event lists before giving them to the calendar.