How can I avoid that my wife’s iPad sounds an alarm every time I add an event to a shared calendar in iCal?
This can be done in the Notifications settings.

How to adjust notifications for iOS Calendar

On the iPad:


Go to Settings
Select Notifications
Select Calendar
Select Shared Calendar Changes
Select Sounds
Select None


One can also adjust several other types of notifications as well or even completely disable notifications for the Calendar app.

Another setting to look at is Do Not Disturb
This can be set manually or on a schedule.

From the settings:


  When Do Not Disturb is enabled, a moon icon will appear in the status bar and incoming FaceTime calls and alerts will be silenced.