Step dad signed a legal document, how ever he fraudulently signed the my decesed mother had no hires. Me and my sisters. Any advice would be very helpful. Thank you much. vince

It depends on what sort of fraudulent document he signed. How do you know about this in the first place? You and your sister have birth certificates indicating that your mother's name is so and so. That should be enough proof to prove she did, in fact, have heirs to her estate.