Sync agenda's

I have made some different agenda's on my iPhone. I am the organisator and share this agenda's with my girlfriend so that we can see who is free of occupied. My Girlfriend did the same and share those agenda's with me. Strange thing is that so many appointments are dubbel in separate agenda's (each agenda has it's own colour). How is that possible?

Wich input is leading, iCloud, iPhone or MacBook?