Originally Posted by ScottGem
Judy is correct about proof. The notary is not going to admit she wasn't in the room, since that would probably lose her, her notary status. A notary has to witness the signature and verify the identity of the signor to put their stamp on the document.
As noted a spouse cannot be completely disinherited, but if your brother recevied some property or assets in the will, the property and home could have been left to someone else.
You also mentioned, previously, that the sis-in-law deeded the property to your brother as executor. But unless the will or a probate court appointed her as executor, she had no right to do so.
Again, you need an attorney to unravel this mess.