My mother has dementia and a believe a family member and a family friend had my mother to sign insurance papers.

My mother has dementia - diagnosed over 10 years ago. My sister took power of attorney from me and had mother sign power of attorney over to her 6 years ago, afterward she had mom signed insurance papers making her the beneficiary (and someone else) something she would have never done if she understood what she was signing. She lived with my mother for only 9 months and afterward, she forced my mother into an institution. We went to court and she was found in violation of my mother's rights by forcing her into the institution. (The district attorney did nothing). Nevertheless, Can I cancel the insurance policy? Or do I have options on the policy? How can I find the underwriter for the policy? My mother has 7 kids and prior to cashing out her New York Insurance policy for financial reasons, she made us all beneficiaries. My mother currently lives with me and has been for 5 years. Her health is declining.