This is really a probate question and I believe you should seek the help of an attorney that experienced in the areas of Estate litigation and Probate matters.
First a gift require donative intent. If your step father didnt know what he was signing, then its not a gift. Second, if the property was community property, your father had no right to give away your mother's half. YOU NEED A CIVIL LITIGATOR to go after your step uncle.
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It depends on whether your step father owned the business as separate property, which may take it outside community property. That would have required a pretty detailed prenuptial agreement signed before the marriage though. Otherwise your mom may be able to fight the transfer due to her never approving it. I don't entirely understand why you think there is "fraud" regarding this transaction, but if your father in law signed documents and was tricked into thinking they did one thing when the actually did something else that would indicate fraud in the inception and may also provide a basis to cancel the transfer. You really should find an attorney to help you. I wish you luck!
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