Can an ex-spouse collect life insurance money if he opened policy without her knowledge before divorce?plus other fraud related?

Life insurance generally requires an insurable interest at the time the policy is put into force. If he bought the policy when they were married, he was under no duty to stop paying on it when they divorced. If he was the beneficiary, than he's entitled to the benefits as long as he meets the other requirements in the policy language. As far as your concerns about what happened in the divorce, you're not going to have much luck reopening this book. Judges rarely revisit property distributions when the parties are alive. You don't have much of a chance of re-litigating these issues.

As for the identity theft, the sons should find out what accounts exist in their names by checking their credit reports and seeing what tax forms are sent to them (generally brokerage accounts send tax forms to report gains, losses, and dividends paid). Once they know where the accounts are, they can access them if they are the true beneficiaries. My father had a brokerage account for me with investments when I was younger. I didn't know what was in there for the longest time. It isn't unheard of for a parent to put investments in a child's name to save on taxes and create a next egg for the child. If this is the case, however, the accounts would benefit the sons. I fail to see where the identity theft is.