Claims against documents signed w/o proper knowledge of contents

Hi, My father attended a marriage recently. There, he was told to sign in three documents, that were purportedly witness papers to the marriage. Given the situation, he did not have much time to go through the documents (at all, in fact). Having signed those three documents, he now is under the fear that one or more of the documents may have been something other than a marriage witness document. Also, due to the troubled relations with his sisters, and that they seem to want to "engulp" our property (they've in person, proclaimed this verbally); and the marriage was the one of his sister's daughter; my father is now worried that signing the documents that day, he might have unknowingly "given away" our property. And now, he is in a miserable state, fearing that we are going to "lose" our land, due to that. Another unconditional fear that he has was that one (or more) of the documents were a document overriding his current/present will, and that his sisters might try to use those documents after his death. Is there any legal measures which can be taken to prevent both of the foresaid cases? Thanking you, Respectfully, and awaiting a quick and favourable response, "a citizen who believes in law".