How can I protect my interest (and my Mom) as one of three Benificiaries of parents estate, not the one that has Power of Attorney or Health Proxy

I care for both my Parents in NY my sisters one 400 miles away the other NC. The eldest got my Dad to sign power of Attorney and Health Care Proxy to her for both of them. Was situation when dads lawyer told me to take dad to bank and transfer $, she went off the wall, told me their finances are none of our Business. That alone makes me think she has something to hide, are we entitled to know or object or is it supposed to be part of the estate. So being Beneficiary not in charge what are my rights to know what's going on, can she just get rid of all Mom and Dads assets (tools, contents of house, money, moms at&t stock) doesn't she have to keep track or account for this. I am the one that is caring for my parents and i am always fighting for help from them so I am not liked very much at all, but I don't think they s/b cleaning out things my god the man is alive. Then i believe Dad will probably pass first so my fear is she will put mom in a home. They had a trust, she had it redone