So, first ensure they're signed on their respective ipads in icloud. Go to settings-icloud and verify what account is logged in. Once you've ensured they're logged into their own accounts open up settings-mail calendar and contacts, and ensure none of your accounts are logged on. Now that you've ensured they are logged on and you're not try getting facetime/imessage to work.
Go to settings-message enter their apple ID and log in. Do the same at settings-facetime.
Let me know what problems, if any, you run into.
I set up FaceTime and Messages on 4 different devices that all share one Apple ID. I added different email addresses to each device as the "contact at" email address and unchecked my Apple ID email address on all but one device. This video explains how to do it.
I don't use iCloud email and don't know why the email addresses will not verify so I cannot offer help on that.
Using FaceTime http://support.apple.com/kb/ht4319
Troubleshooting FaceTime http://support.apple.com/kb/TS3367
The Complete Guide to FaceTime + iMessage: Setup, Use, and Troubleshooting
Troubleshooting FaceTime and iMessage activation
iOS: About Messages
Set up iMessage
Setting Up Multiple iOS Devices for iMessage and Facetime
FaceTime and iMessage not accepting Apple ID password
Unable to use FaceTime and iMessage with my apple ID