[A heavy sigh as Diavolo thinks ... and thinks ... and comes up with no solution.]

Then, I suppose, you are at an impasse. It must be frustrating to be so close yet have no answers. If you do not wish to test their limits, and they do not wish to communicate ... then all you can do is wait for them to reveal themselves on their own terms. "You", I presume, will be pushed to the wayside once more when it happens. I hope you have a plan in place beforehand. If they are as erratic and violent as your story suggests, you must be prepared.