so i went to the doctor that my mother has been seeing for years, i asked the doctor of my mothers cognitive ability to sign any legal documents. The doctor stated that my mothers diagnosis under her care does not have the ability to do so for over 3-5 years of her care. Can my brother still try to execute his part to carry out the will due to my mothers cognitive inablilities
How do you know about it? How do you know she was coerced if she doesn't remember doing it? If she has dementia, it is very possible she is not having an accurate memory of events and dates and could be making things completely up that never happened. This is very common dementia behavior. It's called a delusion.
FYI when a senior goes to an attorney to create these documents, the attorney privately interviews this person to assess whether they understand what they're doing. It is not uncommon for someone with mild cognitive and memory impairment to be deemed competent enough by the attorney to create the documents. Just because your mother doesn't remember doing it, doesn't mean the documents aren't legitimate. It's not the doctor's call -- it's the attorney's call.
Therefore, unless your brother downloaded a PoA template and finalized the documents without using an attorney (which is an option, one that my mother chose to do), then you will need to take evidence of her incapacity at the date of her signing to an elder law attorney to see if you have a case to contest it.
But what outcome do you want? Do you wish to become her guardian? If the existing PoA is not legitimate, and she is now deemed not capable of creating a new document -- then you will need to pursue guardianship through the courts (and your brother could contest this as well). All of which is very time-consuming and expensive.
Your profile says you are burnt out from being her primary and only caregiver... I'm not sure how wrangling for control will help either you or your mother. You have the option to walk away and have your brother (assuming his is the PoA) take over the actual care. You need to do self-care before your health is wrecked by the stress and burden.
Do you care about what's in the will? Are YOU a beneficiary? I know so many piously write that "it's not about the money," which always puzzles me when most of them then describe their bad financial situations because of their caregiving slavery.
I hope your mother is compensating YOU for your caregiving now. And at a good rate. If not, then it seems like your brother has possibly pulled a fast one on you with the will.
Don't you want to extricate yourself from your caregiving situation?
Did you Mother also have prepared a Power of Attorney for her health decisions and finances? If not, it's too late to have that done due to your Mom's current dementia stage.
A Will cannot be put into effect until your Mom's passes, then it is up to the Executor to handle the Will. The only way your Brother can carry out whatever he feels needs to be done right now would be if he had Power of Attorney.