Dementia Interrupting A Will Revisement.

Hello. In brief my mother (V) has dementia. My sister (N) tells me mom has half her brain damaged from the illness. I do know mom is delusional to a great degree and believes her parents are alive even though they have been deceased for nearly fifteen years. She just stares at old photographs and then rants about the stories they are "telling" her.

Anyway, mom has forgotten how to sign her own name and gets beligerant whenever someone asks her to sign papers. Her whole concept of providing ID or how to properly operate a telephone have gone away with the illness.

Would we be able to get an affadavit signed and written up by a neurologist or psychiatrist to trump a previous will she did sign which would split her estate evenly amongst her four children?

The new will would put my 1/4 into a trust fund. My sister told me since I am on Social Security Disability the gov't will take away my inheritance AND my SSD AND my Medicare should mom pass away without having a new will written up and signed.

My mother verbally agrees to the concept or atleast goes along with it up to the point that she is asked to sign. Then when a pen is put in her hand she will rant that her parents refuse to allow her to do such and such. My sister thinks I'm nuts believing that we can get any signed docs to trump a signature.