I am accused of mismanaging mom's funds

My dear mother who just turned 88 has been living with me in my home for almost 8 years. She initially had a spontaneous pelvic fracture, a concussion and broken collarbone and shoulder, and had lain on the floor of her condo for eight hours before I arrived and discovered her. She had a remarkable recovery and due to her financial situation and inability to afford living in an assisted living facility,I asked her to move into my home. She had specific wishes for her living quarters and wanted to pay for them herself. She also wished for me to be her 24/7 caregiver and in lieu of payment she would pay for all household expenses. This arrangement has worked out very well despite my absolute lack of freedom and privacy and an end to my career. I have had power of attorney for mom since 2002. I make all financial decisions with mom's approval and we live a frugal life. The improvements she has made to my house have given us a nice, comfortable and safe home. This last year she has experienced a considerable loss to her retirement fund like many others. To sustain us I took out a letter of credit with my house as security. My brother who has had extremely minimal involvement with my mom has been living under the assumption that my mom is a wealthy woman. He got into her accounts after intercepting the account numbers after her initial hospitalization. He has asked me how much money mom has left on 3 occasions. I have told him to ask my mom since it is her money. I have overheard my mom tell him it is none of his business. This past spring he paid us an unexpected visit and again asked me about the finances. I told him mom had experienced considerable losses but I was doing my best to conserve the remainder of the funds for mom. He called me again and asked me for a detailed accounting of her money and I informed him again to ask mom since I felt he was out of line. I heard him yelling at mom that his "inheritance" was gone. Now, I have been notified that he has filed a complaint with the county elder abuse unit claiming mismanagement of funds. I am dumbstruck. My mother's reaction was to immediately disinherit him and file a new will. I have to go to a meeting with this investigator and she is demanding entrance to my home. How much compliance do I have to give?