My brothers secretly convinced my mother (92), who suffered a severe TBI and now has dementia, to sign over all powers of attorney. Advice?

Signed POA to them without my knowledge. This was ten years ago and wasn't disclosed until my mother became ill three months ago. They want her land for which she and my father worked very hard. My father died 10 years ago after my oldest brother who is a family physician with a questionable record, hid Dad's medical directive and ignored his DNR through intubating him against all legal and ethical practices. Dad suffered for over 9 months and died alone with me holding his hand. My brother has been fired from several medical positions.

I am a retired special education teacher with certificates in 13 areas of special needs including some physical needs. I taught for 36 years.
My youngest brother is a retired black ops/ special ops master sergeant who displays definite signs of PTSD. He was investigated for waterboarding.

I lived on our farm the longest, helped my parents financially, and became their person to call upon as they entered their eighties because I lived close to them. My father told me to trust none of my siblings.

My older sister, was an affluent and once beautiful person, died of alcoholism related illnesses two years after my father's death.

I was asked by my father and hospital staff to provide care for my father since my mother wasn't interested after 61 years of marriage. I did so to the detriment of my personal family's financial well-being. Until my father's illness, I had always been on good terms with my siblings and other family members although they considered my family boring due the fact we don't party like they do.My older sister and brother were born right after WW2, I was born almost 10 years later, and my younger brother was born while they were in college. My brothers have locked me out of the family farm although I lived there longer than any of them. My oldest brother lost his license to practice medicine for three years and blamed me for telling hospital staff. Actually, my father did, demanded they find a copy of his Medical Directive, and placed me in charge of making decisions. My younger brother had taken a contract job overseas. My older sister lived 8 hours away.
Now, I see my mother being medically neglected and have proof of the neglect. My brothers are vicious through texts but won't speak to me. My older brother was trying to get her admitted to hospice so they wouldn't have to pay anything. I found this out through a text they didn't mean to send me. My mother is now in a third class but kind and well managed nursing home near me. My brothers have control of over a million dollars worth of land and buildings through having started an LLC behind my back a year ago while I was in the hospital.The will not sell land for mother's needs.

I am contacted by collection agencies regarding mother's unpaid bills. Someone has changed my mother's address to my home. She lived with us for a month two years ago. 

However, my concern is truly for my mother. I reported this to Elder Abuse in my state. A sarcastic male case worker sided with my brothers, told me this was a family issue, and I really do not know his decisions. I felt like an abused senior citizen when the case manager finished with his investigation.
What are my options regarding helping my mother ? I have numerous financial and neglect records I sent to the case manager. He has ignored them. I would appreciate any advice.