Mom has Alzheimer's but she's in denial. How can I get legal guardianship although my mother won't submit to a physician Alzheimer's exam?

Currently my youngest sister is taking advantage of my mother's mental state financially, and emotionally turning my mother against all her kids. My sister is not giving my mother the medical attention she needs, not preparing enough food for her to eat during the week. I'm spending money on food delivery in between my mother not having any food. My mother is not being properly bathed and had at least three urinary track infections that I know of. My sister has placed a block on my mother home phone so other siblings can not easily reach her. My sister has successful convinced my mother that one of my bothers is trying to kill her. My mother has two security bars, one on the front door and the other on the back door. Both security bars have deadbolts on them. My mother misplaced the key to the front bars and my sister convinced my mother that my brother stole the key. So the only point of egress my mother has is the back door. This is clearly a fire hazard. My sister doesn't live with my mother but comes over a few times a week and definitely by the first of the month when my mother gets her social security check. Currently my elderly uncle lives with my mother but my sister is currently working on my mother's mind to get my uncle out of the house. My sister is trying to isolate my mother so she can continue to take advantage of my mother. I need to get my mother out of this environment. My mother won't submit to a medical evaluation to determine if she has Alzheimer's or not, but I'm sure she does, she exhibits all the symptoms. Can I go to court seeking guardianship with a doctor's evaluation. My mother's life and well being is in danger. Can someone offer me some advice ?