What steps do I need to take get up a Power of Attorney concerning my mother?

I will try and make this short. There are six siblings in my family but my younger brother and myself are taking care of our mother who is greatly showing signs of Dementia. She lives with my brother and want even come spend the night with me. When I go down to visit, I try to spend the night but I have to observe her attitude because she has put me out of the house for no reason after midnight. She won't let her clothes be washed, rooms and bathroom be cleaned. She gets mad when you try to do those things. My brother is there with her full time but trying to get him to take care of anything concerning paperwork is a losing battle. My brother is not working because he is home with our mother and this has caused him some financial hardship. I am going to the poor house financially trying to take care myself and help them. I won't even discuss help from my other siblings. My mother receives social security but hasn't cashed her check in a couple of months because she won't let me take her and a friend to the family was assisting and taking her to do it but she gets mad with her because she told my mother she can't take her shopping dressed in dirty clothes. Of course, my mother gets mad and can hold a grudge for the longest. I have been trying to take her to doctor, eye doctor and help her with her activities of daily living. Sometimes she is so mean to me, l think she hates me, when all I want to do is help her. I know she is 84 years old and having all these issues but the saddest part of all, she has always had a mean streak, it has just magnified since she has gotten older. I am doing all I can to help my brother with my mother because I can see how mentally, it is affecting him. I moved back to be close to home three years ago because my brother told me what was going on and I am the oldest daughter and he needed my help. I know I deviated a little bit from the subject but I had to vent a little bit. Back to POA, the bills need to paid, work around the house needs to be done and groceries need to be brought and this is why I am asking the question. We need help. Also, she won't discuss insurance/burial that's something I am looking into to pay and she will not give me or my brother her Social Security Number. There's so much more I could say or tell but when I come here I see a mirror of what I am going through. Your questions or responses will be greatly appreciated.