Delete duplicate calendar entries on iOS

1. To delete the duplicate calendar entries, one can simply delete the calendar and recreate the calendar setup and then share with Friends if required. This happens sometimes due to iCloud sync between multiple devices and users.

2. To disable the notification on each roster update, Open the Calendar app -> Tap on Calendars → Select calendar (i button) → Event Alerts -> Turn off the toggle.

3. One can open this link by apple Share iCloud calendars on iPhone and refer Turn off notifications for shared calendars.