A Transfer of Ownership is the term to use when discussing with a Customer Service Rep. The individual account holders each need to pass a credit check, and, of course, be prepared to make the move.
Good luck! I co-signed for someone once upon a time that couldn't pass a credit check for Telus. It ended up with me finding out they didn't pay their bills in full nor on time about half way in. I had to buy out the rest of the rest of the contract and cancel it.
The easiest solution would be to pay their share and have them owe you for it when they can pay it. Yeah, that sucks, but depending how much longer is left in the term. It might be the easiest solution financially. If they can't pay their bill on time, my guess is that they won't be able to pass a credit check.