To maintain my overview, I currently copy their content to a separate combined calendar.Obviously, this is quite error prone and cumbersome.I've sent a note to support to see if it can be fixed.
In the Calendar, “Overlay Mode” is such a hidden gem by which you can solve the above issue with ease.
Since I upgraded the i Phone to i OS 10.2.1, the calendar is not upating.
I tried changing the calendar setting from push to fetch and back, and turning off the calendar in the account and re-adding it and neither worked.
Overlay Mode was first introduced in Outlook 2007 after Outlook 2003 introduced Side-by-Side Calendars.
Side-by-Side Calendars is the feature which lets you select multiple Calendars when you are in the Calendar Navigation (CTRL 2) simply by clicking the checkbox in front of the Calendar.