Does a POA have to answer to anyone? How can family make sure their sibling's (POA) spending is legitimate when they don't share info?

My brother has been trying for 6 months to get a MD to say mom incompetent. Without telling her, he succeeded, he is now POA and this has destroyed my mother. All assets were changed to his name as trustee of family trust. He doesn't live near and now mom has no way to get money other than thru him.he says. She now is on a budget.? He is in charge of everything. does this mean not paying me ? . i don't understand why she wasn't told before the closing/change.& what the process was. To take a lady who did all her family's bookkeeping & money management one day & having a great life to next day feeling she lost it all , almost killed her. dementia is progressing but still very clear at times,but apparently all her MDS didn't feel it was time to sign saying incompetent but unfortunately he got to one who doesn't know her only by the hospital visit for pneumonia. I feel he is acting rude,unjust and insensitive. Had she known he was to do this they could have worked it out together. She says she never wants to see him again she had been depressed since my fathers death but now she has deteriorated in health and has been sick with worry and anger. I have been her live-in nurse/caregiver since 2007( started with my dads health )but when he died 2011 her dementia began. We knew someday this was coming , but not this soon he should have let her in on what he was to do like close accts,credit cards. etc She cant see her accts balances now,worrying He has all power but cant be reached lives 7hrs away. I now have lost a job my best friend and living arrangement, he says he cant pay me cause "they wont let him" Lawyers? She had plenty money.Is he lieing to me? How can I find any information what is happening to our lives? i am perfectly capable as a nurse but if he is hiring i should be a part of this or is he planning to place her? WE promised to keep our parents home as long as we could care for them....... Mom & I are devastated, very suspicious,hurt, very angry Any suggestions.I will be using my savings to care for her temporarily till something happens..How can we see if he is spending her money??? Who watches a POA?