There was this old man who passed away a few weeks ago. He had diabetes and his doctor since many years ago had forbidden him to drive or even self inject insulin. His wife took care of him. In that period his step daughter gave him some letters of authorization to sign and he did. Now turns out to be that those letters of authorization benefited financially the step daughter only and left the spouse out completely. Is there a way to annul those letters of authorization?

The wife will need to hire an attorney, depending on what the man signed, and the county ( and if US the state) in some for example, you can not leave the spouse out of a will and so on.