My family seems concerned about inheritance and are fighting for Mom's assets. Any advice?

My "family" has been torn to shreds because my Mom got VERY OLD. There were 7 siblings... one died... 2 were POA's who prematurely put her into a nursing Home 2 yrs. ago. The remaining 4 decided it was too early for her to be there, drugged to keep her quiet etc.; so we took her out of there and took turns caring for her since then. (She went straight to an attorney and fired them as POA's PLUS took them out of her will!). She appointed "her favorite" dependent son who lived at home with her until he was 35 as the new POA. The first year, she was able to walk, see, hear with hearing aids etc.
As her condition began to deteriorate, the favorite son and our mother's "favorite grand-daughter" began to manipulate her (the son taking a box of cash & old silver coins home to "watch for her". This aroused jealousies and suspicions. Not being very capable of doing anything, due to being spoiled by his favorite status; the POA son began demanding certain things to be done and was highly critical of "how" these frivolous things were done... Mom always upheld him in these commands and he felt confident with Mom and the grand-daughter making life as difficult for the remaining 3. Living 130 miles distant from Mom's and driving it every week 2 days per week... then home. I began feeling "left-out" and abused. I spoke to a therapist who suggested that I cut my time in half with the caregiving. By doing so it put pressure on everyone else, but I felt quite overwhelmed by the constant suspicion, fighting, arguments etc. ; so I did cut my time in half. This brother decided he would not "relieve me" when he was scheduled to do so... as punishment for cutting my time there.
My "other brother" had been taking care of Mom's finances... and doing a very fine job until several weeks ago, when: the POA brother suddenly took control of the checking account, blocked my brother from getting funds and even blocked my mother from the account.
My mother said she wants this "other brother to continue paying bills, buying groceries and etc... BUT my "other brother" walked out after making appeals to him to return the checkbook , ATM card etc. Needless to say the POA Brother would not comply with my mother's wishes.
My sister who bathed Mom and took care of her 4 days per week quit because of the POA Brother's demanding and criticisms.
SO, now the POA Brother is alone with my mother. Does not allow my mother to speak to any of her other children on the phone, changed the locks on the house and is very much prone to paranoia... has an axe at one door, and a pistol in the house.
He told my sister "We will be sorry that we 'walked-out' on Mom." (I believe that to be a reference to the Will.)
He really has been unstable, jealous of his siblings, very paranoid and reclusive.
I believe he is neither capable of caring for Mom nor being her executor either. Does anyone know what is the right thing to do.. especially, since my mother is behind him all the way (she worships him! But he has made her as paranoid as he is... and her dementia is now extreme... she can't walk, looses her balance etc. He don't cook but feeds her junk food.)? Now we can't even visit her, nor call her. I just feel like walking away after 4 years... and it's probably what he hopes I'll do. I just feel angry at him because, for him, he thinks he can do as he pleases with her will after her death, now that he has run everyone away.
If anyone has ever been involved in such a twisted mess, please advise me.