Google Calendar, iOS, and Mac OS

I have a question, but first, let me explain the situation.

I have around six different calendars that I keep up with at any given time. For years, there has been no problem adding, removing and syncing events to my iPhone or Mac Book Pro… ‘Til now.

In a few days, I will be bringing on an assistant to help with various tasks and needs that I have around the business. That being said and with collaboration in mind, Google Calendar looks to be THE solution for us. I want to be able to plug in events on my iPhone and have my assistant be able to access them on her phone or on the web. 

My question. How may I post an event on any of my six calendars from Google Cal, iOS iCal, or Mac iCal and have it sync across the board as opposed to having to post it just to Google and only being able to read it on iOS and OS X?

EDIT: I have looked into CalDAV, but I have not been able to set it up in a way where I can have all access from and to any calendar I please. Thoughts?