<human>: Can you condense the text into three sentences or less?

Hi all, 

I'm writing on behalf of my 80 year-old grandmother, a U.K. native who's lived in the U.S. (MD) for ~30 years now. Most of her family is still in the U.K., which is why this question concerns the law over there. Kind of a complicated story: 

Just a few weeks ago, her older brother (Let's call him Charles) passed away. He was 82 and lived alone, as his wife passed away years ago and they had no children. About 6 weeks before his death, (this is where it gets weird) his wife's estranged step-brother appeared to "help" and take on a caretaker role. Prior to this, they had not spoken in years. 

After his death, we found out that the step-brother (Let's call him Dave) is, for some very odd reason, the executor of the Will. The will was written in Charles' home and witnessed by a notary, but no lawyer was present. In the will, the entire estate is left to Dave. This wouldn't be as weird, except Charles had repeatedly assured my grandmother and her sisters that he would "make sure they were cared for" when he was gone. We also have doubts about Charles' mental state towards the end, when this will was created. Also, Dave is refusing to share a copy of the will, despite several requests. This reeks of a con to us.

Basically, the question is regarding what legal ground my grandmother (as next of kin) has to support appealing the will. What kind of proof is required to overturn the will? She is planning to go to England if necessary, but since she's also not in the greatest health she would like to make sure there is a possibility of results.
<bot>: How can next of kin contest a signed and witnessed will in the UK.? What type of evidence is required to change a will?