Mother in denial, sister and nephew block efforts to obtain intervention for my mom?

My sister and I live with my elderly mother.Due to dysfunctional family issues with my mom in center my sister and I do not speak to each other. Despite emotional and mental abuse I have always took care of my mother since in my youth. When my father died I took over groceries, cleaning, maintenaince while my sister had yet to pick up a broom or buy anything for the house. She was spoiled like my mom. Now as she ages those same forces are at play but stronger. Neither my sister or mom have ever been able to acknowlege the love and work i have put into family. I made holidays big for our children she had 2 boys I have one. My mom and I raised her two when her boyfriend didn't allwow them in. This same nephew I helped raise and his mother are now actively blocking every effort I do to help my mother. Once when my mom was really stuck in a moment of dementia, I called my sister and asked her where to take my mother because the Hip center was closed. She called my mom and I heard her say on phone don't give D none of your papers or information. Now they are making it seem like im inviting people to my moms house with out her consent when im trying to get the meals on wheels program for her which she had before. My mom is almost cachetic. It hurst to see her. They are in denial my nephew txt me saying "she does not want meals on wheeels. Please respect her wishes and she does not want the Lady coming to her home no one should be inviting her to come inside her home without asking her. Shegettting unnceccessary strees from the everyday drama and it has to stop. Ma is just fine just let her be" I am the oldest although we have a crazy relationship I am the only one who keeps it real. When she gets the meals she is happpy. she has never told me she dont want it. she acts like its her boyfriend when the guy rings the bell and she eats like its a date. Now I reopened the case after postphoneing due to their oppostion. Said I d see what they do. I went to see my son when I came back the frig was still same except for juice. All the pots are burned. the bills are backed up behing. I tried to communicate with my sister thru a letter that we need to come together for her optimal health and she wont let me but maybe she could try and get her bills together cause she not paying them and then when the next one come she dont want to pay it cause its too much. The other day the cable went off. My sister who went to store with her went straight upstaires. I met her at store saw my sister was helping so I told her I would see her at the house. I always put away her groceiries even when she was able. My sistee dint know cable was off. I have just got back to work. I work nites. Getting back after years not working when I became ill s/p WTC 2011. I had to move back in. When I did my sitster locked her bathroom door. MY mom didnt want me to watch her tv while in was in kitchen coooking or use her phone. I had nothing. and nowhere else to go. But Im saying my sis didnt even know tv was off . she not obserant and feels becuae I live there I am responsible to clean up and do all. I been cleaning and being called triflling by my mom all my lif while her and my sister layed up and teamed up to belittle me. I intend to carry on with the appointment to continue with meals on wheels. If she dont want it trult the she can say so then. But how do I deal with the animosity and hinderince of care for my mom by my sister and nephew. My son an I arre the only ones who clean and buy appliances. He is moving again to Cali with his family and is expecting another. He came weeks ago and threw out 15 bags of trash and we got her a new fridge. She has locked me out in past for no reason and when I ask its always something that doesnt come together. She needs stove but Im afraid to invest anything cause I may be locked out tomarrow by her or my sister if she could. How to I handle this. Please advise. Its painful I pray, I watch my mother dwindle while i live the bitterness she has created betwen me and my sister. Help.