re: Doubt this has happened to a TDer before.

There is no greater love on earth than that of a mother and her children. To give up a birth child for his well-being is probably the strongest form of love there is. Your wife is to be hugged. Three kids lost their dad, wait awhile so they don't feel shocked times two. Then take the original returned letter and write a new one explaining it was returned; and mail it certified mail-with signature required- to the widowed wife of your son. There is no reason why they can't have two sets of paternal grandparents- make this very clear in the letter.

Logic prevails, he had to have known from his BCert that he was adopted. If he didn't know his kids need to know.

ETA: Every time we go to the doctor they need family history. For this alone I think biologicals should be known. I could not imagine going through life not knowing biological relatives.