How do i find out about father's life insurance policy?

Father and Stepmother were in process of divorcing, but father died before everything was final.He purportedly changed his life insurance policy to include all of his children, not just those bore by him and stepmother. He sent the paperwork in the mail. Never heard anything and stepmother has everything because father's new will wasn't finalized...It's been three years. What can I do? How can I find out which life insurance policy he had and do we stand a chance of getting any of the money if the insurance company simply didn't process the change before he died?