Do I have any right to stop my older brothers from depleting my fathers account money?

My father suffered a stroke five years ago that left him unable to make financial as well as day to day decisions. My elderly mother took over their finances. She is not capable of this responsibility. My father took care of everything regarding their finances their entire life. She is also from Japan and has severe difficulty in understanding the written content of contracts as well as other financial documents. My two older brothers have begun depleting my parent’s finances due to my mother’s lack of any financial education. Over the past five years they have milked her for over $500,000.00 minimum that I am aware of, but fear the amount may be much greater. One of my brothers even went so far as to obtain credit cards under my father’s name, then proceeded to run up over $100,000 dollars in credit card debt that my mother was forced to pay to prevent my father’s credit being damaged. He also talked my mother into giving him power of attorney over their assets (citing her inability to handle the finances), then sold off a large amount of my father’s stocks and took the funds made from the sales for his own personal benefit. My question is this: do I have any legal standing to step in and prevent them from completely extinguishing my parent’s portfolio, as well as my share of inheritance?