I really feel for you and know the frustration that you are enduring. I fully understand the time, resources, and personal strength that it takes caring for a member of the family with PD. I also know what it is to be the only child that remembers “mom”. Don’t give up home and maybe your siblings just can’t face how your mother has changed with this disease. If family members live close enough by, maybe you could invite them over for a Sunday pot luck get together and have “mom” there also. Don’t try to push her on anyone else just let them get used to her. (them being around her might help them understand what its like to have PD.) Try to keep the get togethers at a non emotional level and the communication lines open. I know some days I just want to go running down the street screaming and pulling my hair out. However after these thoughts pass I know that the day will come when my own mother will pass and it will be a time of sadness and joy for me but for her it will be a time that she no longer has to suffer the effects of such a horrible disease. It helps to have this forum to vent about the things that are going on and to have the support of others that are going through the same or have been through the same things. Good luck with your mother and family. I hope that all works out well with you and yours.
P.S. as for any legality I would contact a local attorney and even a local Legal Aid Society chapter might be able to help you.