To me, getting the facts wouldn't solve the problem.  Neither would dwelling on what should have done or could have done.

To me, at this point, it is NOT YET ready to discuss the tax issues.  If I were in your boat, I would advise the sons to get competent legal advice, from an attorney specialized in estate and trust for the state (you said NY?)

Issues would include:

probate needed?

Disclaimer possible?

The options for the inheritance and distributions? 

Once the family obtain the legal opinion on the options, analyze the tax angles for each.

If there's only ONE option, still analyze the possible tax angles.

I imagine the legality involved could be different from state to state.