Words can't describe how I'm feeling when I started to see suspicious bank transactions from my brother/sister in law.

My mother and I live together in her home for many years, which never was an issue until I began seeing a decline in my mothers mental state. Although 88 yrs old, to anyone else you would think she is fine. My brother was the one taking her to the doctors appointments, and my mother wanted me to handle her end of the bills to the home. Never had any issues other than when i started to see suspicious activities with moms checks written out to my brothers wife for "school functions" for my niece. I do my homework when I investigate if something doesn't look right, because especially with family "we" dont want to accuse without facts. In the past i have caught my brothers wife lying about monies needed for school things, asking for more than what it actually costs etc.
As time went by mom and I set up auto direct deposit to go to her savings account which I have no access to it of 100 each month so that she could go visit japan where she is from etc. In the meantime I began this in April 2020. My brother was added to moms accounts as co owner at that same time, I didnt think anything about. I began seeing checks being written to my niece just about every month some months 450 give or take. I only would pay bills, or at times if I had to put my own money into her checking to cover the shortages (usually due to 2 to 3 checks ) written out to my niece for things. As for my moms saving account, i can see that Online transfers from her savings was going back into her checking account. I know that I couldnt do it since I had no access only to her checking. The first four months Online transfer to savings is what should be done. Well needless to say, she had only 120 in her savings. I asked my brother about this and he wasnt listening to me and tried to turn all this on me stating that I was taking the monies.
I was disgusted with his accusations, all of moms statements were changed to paperless, a box of her checks were shipped to his house, while on vacation and i took mom with me, during that time door dash was placed not only once, but over 294 dollars worth. I contacted the bank they reverse the charges but yet no accountability (since he was added as a co owner of her accounts). I know i had several mental breakdowns, and while i was down, my brother laughed at me. This infuriated me. Backed into the corner, I contacted the police, they said get an attorney for the matter, i contacted an attorney they said basically co owner of her account is the issue. I got a durable POA which i submitted to the bank, but after all this and i left out a few other incidents, Im surprised i didnt do anything stupid that would land me in jail. The worst part of this all my mother is very partial to my brother he could do no wrong. Im just trying to help her stay afloat with her finances, Im lost for words, as you can see lol. I feel betrayed, played, lied to, even turning this on me? no way i already changed my bank cause i dont want my name on her accounts, i just paid the bills she needed to be done.