Is this considered elder abuse?

My father and his live in female friend lived together for many years. Female friend is much older than dad and passed away last year. Dad has been diagnosed with dementia last year. He was fine in his home with his female friend there. When female friend passed away my brother though it necessary to take him out of his home without consulting the rest of the family members. I thought this was temporary arrangement, living with my sister until arrangemetns were made for assistant living. However when brother realized that assistant living would cost money, he and another sister was totally against it. They had their eyes on dads money for some time and they devised a plan without the consult of the family that they would care for mom. I continued to look for an assistant living community. I felt it would be best for dad. He would have his independence, medical, his money, visits from family members and socialization with people his own age. This never happened. During the time that dad resided with sister she was able to convince him that in the assistant living, the aides beat you. They convinced hm that he would not enjoy an assistant living facility. Therefore, he remained in sister's apartment. Everything was going along O.K., I thought until I saw various suspicious account acitivity. Dad is not capable of handling his finances. The first suspicious activity is that my dad added my brother as a joint account owner to his life savings, This is a brother that my father did not trust with anything. He has gone bank rupt two times and cant handle his own life to well. He smokes marijuana and keeps company with ex-felons. Now all of a sudden he is a joint account owner. it gets better. As time goes by my sister finally realizes her heart isn't in it to take care of dad and she and my brother decide to obtain Medicaid without consulting family members. They have dad give his life savings to brother. All of this was done with my dad while he has dementia and really does not understanding what he had done to himself. I went to the bank with dad and looked into his accounts that is when i realized what my brother had done. My dad was so angry he did not remember signing over his life savings to my brother and tried to get it back only to be told that his life savings no longer belongs to him. My brother now has control over his money. My dad was very sad and started crying. He asked me to help him get his money back. I said I would. Dad also stated that he does not want medicaid and he does not want any home health aides in his home. He wants to live with his family members and he has family members who are willing to care for him. I believe this was a scam by my brother and sister to take control over my dad;s life savings. In addition, my dad's apartment was still being paid for by brother who is not POA. Dad has not lived in his apartment for about a year. My brother has made my dad appear to Medicaid as if he needs home health care. It is my sister who can no longer take care of dad. She uses the excuse that she has to find a job. She is a high school drop out that has been layed off. she was offered a job once at her old job but with lesser pay, she refused it because it wasn't paying enough. Brother states that sister needs to find a job and is unable to do so with dad in her apartment. So they lied and said that dad was still at his home so that he could get Medicaid. Dad has family members who wants him to reside with them and they will care for him. I believe this was a ploy for brother and sister devised to get control of dad's money. The bank said that dad's money is in a trust with my brother's children as beneficiaries . My dad said that he wants his money back. They tricked him using medicaid as the excuse. How can we get dad's money back and get him away from his children who do not have his best interest at hand. Dad worked all his life. He deserves to enjoy his money. Dad is retired and has a pension and SS. I want to help my dad so much. What can I do? He has lost everything he worked so hard for. One time I had my dad, I noticed he had a black and blue mark on his arm. When I picked up dad again he had another black and blue mark on his arm. I did not consult my brother because he, my other sister and I have had extremely bad arguments in regards to them trying to keep secrets about what they are doing to dad. I have tried to keep me out of the loop becuase I do not agree with what they do. My dad is nothing but a money bag for them. They prey on his incapicitation and his dependency. What can I do to halt this situation. He wants to be with me anyways. I truly have my dad's best interest at hand. Would guardianship be an option? P.S. I have POA.