I'm not surprised he shuts down when you ask him questions...they are paranoid and everything is a secret to them. So, what do you do? Listen to what he's saying because they have loose lips and he will tell you in a roundabout way what is going on.

Now about the kids, you do need to find out why he's grounded them and go from there.

Sometimes the meaningless chit chat will give you the clues to whatever you are wondering about. You'll know if it's meaningless or not.

Sit quietly, the answers will reveal themselves when you least expect them to.
The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.