Suspect sister and her husband are stealing from 70 year old Mom. What do I do next?

My mother is very ill. She is on oxygen 24/7, dialysis, diabetic and congestive heart failure, memory loss and Lung cancer. She gave power of attorney and financial responsibility to my sister in another state who has served time in jail for fraud, stealing checks and computer fraud. My mother did this within a month of my father dying despite recommendation from nurses to not make any major life decisions until 6months after his death. She was always taken care of and had no responsibility during her life as my father took care of everything. My sister and her husband who never spent any time with my parents moved in on my Mom after his death and took over everything. Since then they have built a new home, bought new cars, paid for three of their children to go to school, paid children’s bills, etc. it is very suspicious to me because they had Mom sign power of attorney, move money around to different accounts, over the prior years and got three cars from my parents which never was paid back. I made a report to elderly abuse here but they dismissed it without checking into it. What can I do now?