Sync multiple calendar together
I use BusySync... overall it works well.  It certainly accomplishes exactly what you're talking about.  I have several thousand events on my calendar, which appears to corrupt the database from time to time, as I have BusySync conflict issues, as they're called.  These errors are rare, and support from the company has always been a) speedy, b) comprehensive, c) able to solve the issue. I spent a substantial amount of time researching this years ago, well before iCloud and BusyMac were available... but at that time, BusySync was the only reasonable choice.  Since then, I haven't switched, because this solution still works well.

I recommend BusySync or BusyMac... both work the same way, it just depends which environment you prefer.

While you could use BusySync to host on a local server and that would be fine, working through Google is easy, free, and compatible (you can sync with other machines that don't use iCal or BusySync).  Google also allows for an easy web interface on the go, mobile integration, etc.

I hope that helps.