I agree with Martha.... it takes a court order to declare somebody incompetent. Even in the later stages the most we have done is declare Mom incapable of handling her own financial affairs which is very different from from being incompetent.
We had much the same problem with Dad's will. Mom had the wills redone at a point where she was in the early stages of Alz and Dad had mid stage Vascular Dementia. There were some problems with the new will. Yet when the lawyer saw both wills, knowing of Mom's early stage alz and Dad's dementia, we HAD to use the most current will. Through family agreement we should be able to "fixed" the problems.
I can only assume that the children that got less in the new will are not happy with the equity in the new will. Each state is a bit different but they could protest the will and hang it up in legal proceedings but I don't think they would do anything but make life miserable. Usually the judge will go with the final word of the person writing their own will
Hopefully this helps... and good luck. Family squabbles are not fun