How do i stop sacrificing my life and happiness for 2 eldery parents...desperate please help?

I'm a 32yr old female. My mum is 69. I live two hours drive away from her with my partner. I'm an only child. I had to move 10 yrs ago (from near her) as she was haring me, dropping into my workplace and making life hell. She has mental health issues and as a 22yr old i found it too hard to deal with, the embaressment and shame. Shes under psychriatic care. She was living fairly independantly but now her behaviour is really bad, shes impossible to be around, causes trouble with family members any way she can. I cannot bring my partner to her house to stay. She hates him and refuses to acknowledge that we are a couple. Her underlying belief is that i should move beside her and 'take care of her'. She is obsessed with this belief and drives it home to me 100% and tells all that will listen (neigbours,family and all ) that i dont visit her much or that she doesnt see much of me. I ring her 3 times per day, i visit her alone every 3 weekends for the whole weekend. I do anything practical for her that she'll let me do. Shes a tremendous bully and does not behaviour well. Would think nothing of insulting someone's dead mother to their face or saying awful things about me or my father, thats even after i lovingly tell her to refrain from such comments and she will have a nicer life. All her relatives have abandoned her, no one visits and even the neighbours want nothing to do with her as shes dangerous as in she repeats anything she hears and names names. Like a 3 yr old. But very malicious gossip. She hasnt a good word to say about Dad and subjects him to horrendous verbal abuse.My dad has his house half hour drive away. He stays wtih her over night. Arrives at 7-8pm at night and leaves around 10am in the morning. Spends the whole day away from her. I was raised with her and her foster mother. Life was never easy. She stood out for her bizarre behaviour, i dressed her from when i was a little kid and i was bullied very badly coz of her.Dad lived most of the time with his brother who was mentally handicpped. My mother i feel right now, needs more care. My father refuses to acknowedge this. He does not want her 'instituationalised'. I dont wish her to be 'locked up 'either, but i think she needs more care at this stage. He will not let me speak to her psychitarists or nurses in charge of her. He says that she 'cannot help her behaviour and that we ahve to live with it'. He says to me when i tell him i'm stressed ' cop on to yourself'. Yet, he will not reveal to her health professionals exactly how bad things are. He expects me to 'visit more' but even that does no good for her or doesnt make her happy, even though i sacfifice so much of my happiness for her and to 'make life easier' for dad. He tries his best with her. My life is so controlled i cannot tell her (or him now) i'm doing something nice for the weekend or they try to make me feel so guilty. Dads tone would be 'good for you, what about me and your mother'. I've put off getting married coz i know she would go beserk and there is no way you could have her at a wedding, she would rise hell. I spend all my xmas and easter holdiays with her (all my life)..alone without my partner. I'm so stressed i'm on medication and seeing a therapist who is trying to show me to set boundaries. I've told my dad this and he says that it is 'my problem', the way i look at things, that 'your mother cannot help it, and you have to live with it'. Its not that i cannot 'accept' shes ill, i fully do. I just cannot accept my life being a slave to this illness and her controlling behaviour, thats the problem. I want my mum in my life, i love her, and love him, but i'm sacrificing my life and they control it. To the point i think its not work living.I tell him im worried sick about her and him and he tells me to cop on. He has multiple health issues aswell so i worry about him so much. Please advise me. My lifes very difficult and i love and care for both of their welfare. By the way shes well known to a psychtiratic team but they tell my dad and me theres nothing that can be done for her. I do speak to her psychriatic nurse and doctor and have told them how much stress she is but they say 'thats just the way she is, that she is just akward, and that they cannot help her'. So therefore dad doesnt want to take it further. Dad doesnt want to discuss this with me. I ring him daily to get monosolabic conversation from him.