our situation is similar. we have a Windows 7 desktop and laptop and an iPhone 4S and an iPhone 5. we use Outlook on the PC's for our calendar and the native IP calendar app on the phones. I wanted to enter a calendar appointment once on any of those devices and have It propagate to all of the other devices without human intervention. as you may know you can sync the iOS calendar to each phone thru the cloud but the issue for us was having those calendar appointments flow into and out of Outlook.
after many experiments I finally found the solution...
Companionlink. this does what I want it to do flawlessly. it works this way. I set up a free calendar with google that acts as the "middle man". then I configured the iPhone calendar app on both phones to read and write to the google calendar. after installing Companionlink on the PC's I did the same with it...reading from and writing to the google calendar. when I make a calendar entry on any device it copies that even to the google calendar. every 5-mins all of the devices...the 2 PCs and 2 smart phones...query the google calendar looking for new events to download, existing events that have modifications and events that have been deleted and the necessary changes are made on all devices.
check the website and give the company a call. they were super helpful getting this set up.