How can I prove my 99 year old great grandmother with dementia is being financially abused?

My great grandmother is 99 with dementia dating back to 2016. My cousin has been keeping her away from the rest of the family and has even changed her POA to himself. He's added his name to her bank accounts and also has bought a new $550,000 home with her money for him, his wife and her kids.

My great grandmother previously had a will done in 2006. The new estate lawyer my cousin appointed for her, states that the old will is no good and not valid. After many family members attempted to call or see her, he had my great grandmother put multiple restraining orders on everyone suggesting that she's scared of them. Now no one can call or visit her. Is it legal for her to have a new POA or will if she was diagnosed with dementia in 2016? Can this be appealed?

While cleaning up a room in the house an old phone of his was discovered. After searching through the phone, there are many videos he had taken of himself asking my great grandmother to be her POA. There is even a video that shows my great grandmother signing Successor estate and trustee documents, leaving everything to him and his wife. In many of the videos, which she had no idea were being filmed, she can be heard saying that her memory is very horrible and she forgets things all the time. Her new estate lawyer, who is looking out for the interests of him and my cousin, states that she is perfectly fine to sign the documents and she knows what she is doing.

Also, bank statements have started showing up at the house about my great grandmothers account. There are penalty letters from Chase about too much money being moved from savings to checking and even information about going over limits. She was never the type of person to spend large sums of money. My grandmother has a court date on Oct. 31 to appeal the restraining order placed against her by my great grandmother because of my cousin. They state no new evidence can be brought up at this hearing, but the videos on the phone and bank statements weren't found till after the first case. My question is, what can my family do to stop my cousin from going through with this process? At the last hearing, his lawyer presented paperwork to have all of my great grandmothers property and houses go to him as a trustee once she's passed.

Visits and calls have been made to APS(Adult Protection Services) and the DA, however no one has gave us clear information on how this can be resolved. Any help or advice on this topic would be greatly appreciated.