Question of will fraud

My mother-in-law revoked a trust 12 years before she passed away in 2007. The trust agreement had been broken by her oldest son when he did not follow the terms of the trust. Prior to the trust being revoked and a new will being written the son had an extra marital affair while his wife was dying. Also, my mother-in-law questioned some of the financial transactions conducted by the other son in regards to bills and other transactions for running of her farming operation. When she changed her will it left minimal property to the oldest son and the majority of her property to my husband. My husband did what was request of him over the entire time in question and caused her no reason to doubt his loyalty and trust. Now the older brother is claiming fraud in the creation of the new will. There was no fraud committed. What would they need to do to prove fraud occured? According to the judge there has never been a case of will fraud tried in Nebraska. This is a case of he said, he said, therefore she acted upon it but my husband was not the one to question the financial practices nr was he the one to inform her about the extra marital affair. The older brother had not had anything to do with his mother until after she had died and the will was filed.

The fraud allegation will not stand up.

She made a will and if she was competent then he has almost no chance of overturning that document.

It is very very hard to do so even under quite strong facts, and such facts do not seem to exist here.