I will be setting up one apple id to use for all the apps for all my three kids on their three ipads, will they be able to facetime each other using the same apple ids? Or do I have to create different ids for them in order to facetime each other? Thank you.
You can use the same apple id. Just add unique special email addresses to your apple id.
This link explains it nicely. http://ipad.about.com/od/iPad_Guide/ss/How-To-Use-FaceTime-On-The-iPad_2.htm
So far so good. You end up with ALL email addresses (that is your initial email address associated with your Apple ID AND all additional email addresses added under Settings > Facetime on any of your iOS devices) listed on EACH device (linked to your Apple ID) both under Settings > Facetime AND under Settings > Messages > Send & Receive.
You still have to select the desired email address on each device, both in Settings > Facetime AND in Settings > Messages > Send & Receive. And you possibly have to deselect any email address that previously was selected per device (e.g., the email address associated with your Apple ID that would be selected by default).
Do some testing by placing Facetime calls, and separate testing with iMessages, across your various iOS devices to be sure that you got it right.