Twenty years is a long time and statute of limitations may limit what they can do.
Hire an attorney if you receive a letter of their attorney.
The answer given does not imply that an attorney-client relationship has been established and your best course of action is to have legal representation in this matter.
There is not enough information here to give you a decent answer, and in any event, you really won't be able to know much about the legal posture of the case and the options you (and they) may have without sitting down with an expert Wills lawyer, reviewing the documents and allowing him or her to interview you with respect to specific facts.
If the Will and the pre-nup are old, they will probably stand up and be enforceable. I would suggest you consult with an attorney now so you are prepared if they choose to advance any claims against his estate.
Mr. Huddleston is an Ohio-Certified Specialist in Estate Planning, Trust & Probate Law, with offices in Columbus and Dayton, serving client families and private business owners throughout Ohio. He may be contacted directly by phone toll-free at 888.488.7878 or by email CLH@HUDDLAW.COM. Mr. Huddleston responds to Avvo questions as a public service to help educate and provide general guidance to questioners, but his responses are not legal advice and do not create an attorney-client relationship.