Any advice please!

I'm caring for my mom who is in her 70s. She has been diagnosed with Alzheimer's and dementia. She recently has been diagnosed with major depressive disorder with psychosis, paranoia,and agitation. I have siblings who are in denial and fight with me over the care her doctor recommended. I'm her DPOA and they do not want to respect her wishes and fight me on everything. I don't want to have guardianship of her but I don't know how to protect her otherwise. They keep telling her lies about me but I don't even really talk to them. Me and my brother have not talked in 8 yrs+. They are causing her to get upset easily and I don't know what to do about them. My mom calls me crying when they put me down but when I tell them to stop saying things in front of mom, then I become the "bad" guy. I worry about this stress on her and her mental status is not good. They refuse to accept what the Drs say and get her into our disagreements. To them they think she can still make good medical decisions and life decisions even after being in a psychiatric hospital and the psychiatrist saying that her paranoia and agitation is so bad she can't make good choices for herself. Please let me know ways of coping with this. She says that if they keep it up she's going to prevent them from seeing her but I know she loves them and wouldn't really want that either. They are toxic to her health but they are still her kids.