My mom has dementia. She suddenly wants to change her will. I think she is being influenced to do so by my brother. Any advice?

Techie gave you an excellent answer. Crucial to your questions now: you say you are BOTH POA. Has she been declared "incompetent" due to dementia IN WRITING. If this is the case, this is something you need to get a copy of from her physician or her neuro MD. Having this will negate wills made after the current one (which you should have a copy of if bro is heading in for the money). I agree with Techie that with this level of dissention you may BOTH be taken out of any conservatorship or guardianship if it comes to a fight. At that point the two of you, either or or together will have ZERO to say about ANYTHING including care and placement going forth. Take care. See a lawyer (Elder law) on your own now.

Many people upon a dementia diagnosis are advised by the doctor to get all "affairs" in order while still competent, including updating a will. If your mother is still competent, then a guardianship challenge will fail. If your mother's doctors have already deemed her incompetent, then a guardianship may succeed; however, the court may chose to appoint a third party since you and your brother are arguing unless another family member (your mother's siblings or your siblings) endorses you. If your mother's doctors have already deemed her incompetent, then she cannot make a new will.

I suggest using your POA to find out whether your mother's doctors consider her competent before taking any other steps. If you can get a statement of incompetence from her doctors, you do not need to fear any new will because it can be discarded by the probate court following your mother's death when you present the doctor's statement.

I recommend only filing for guardianship if you and your brother cannot agree on your mother's care. If you choose that route, make sure you have a plan for your mother's care to present to the court. When contesting my father's guardianship my brother told the court our father wanted to remain in his home and he wanted to honor our father's wishes and since he was the only child willing to honor our father's wishes Dad had recently made a new will (12 years after being deemed incompetent by doctors) leaving everything to him, disowning his wife and other children. I told the court our father needed 24/7 care which we could not afford to provide for every long in his home; however, if we liquidated our parents assets there would be enough to fund my father's MC care for 10-15 years and enough remaining for 5-8 years of care for my mother too. Dad's heart doctor endorsed MC care and my mother and another brother stated they preferred me as guardian/conservator; the court agreed and granted my petition.