How to manage duplicate events on iCalendar (Birthdays, Flights Confirmations, etc)

I'm running into a frustrating issue with duplicate events on my iCalendar, and I can't figure out why and where they're coming from (source, i.e., Gmail, iCloud, or Exchange). I really don't want to delete the calendars that are associated with my different emails, but these duplicates are cluttering my calendar and making it hard for me to stay organized.

For example, my brother's birthday appears four times on April 1st. 2 entries incorrectly state that he's turning 27 and are the same but appear twice. 1 entry uses the name I have for him on my phone with the right age, then lastly, there is the purple "birthday" one. The screenshot is below. The same thing also happens with flight confirmations. I'll check my calendar and see multiple entries for the same flight, each slightly different, though, and I get confused about which is the right one with all the information I need.

1. How can I tell which calendar or source each event is coming from?
2. How do I know if its all syncing properly across my devices?
3. Is there a way to detect and clean up duplicate events automatically?

Any insight would be appreciated—this is driving me nuts. Thanks!