HOw can i deal this utter control from 2 elderly parents, one being mentally ill?

I'm a 33 yr old female. I'm the only adult child of a mentally ill mum. she is 68 and has her own house. She is psycially well, drives her own car and attends day care and is on medication and under supervision of psychriatic services. My dad does what he can for her. He has his own place half hour drive away. He stays with her every night and does whatever practically has to be done for her. she is verbally and emotionally abusive to me and to him. I live 2 hours drive away (could not live near her, was 10 yrs ago and she was haring me). I ring her three times per day now and i spend all my holidays off work with her. They are not a holiday, they are torture. She says its 100% my role to 'look after' her and makes me feel so guilty. I stay every month wtih her for a full weekend. I also have a partner i'm living with for 8 years and he is neglected. I canot bring him to her house, she is jealous of him and is nasty. She was hospitalised for the first time in 10 years two weeks ago. I visited her all last weekend. Now she is coming out and wants me to go home and help her settle in. Yet when i'm leaving she will throw tantrums. My dad wants me to go stay with her for this weekned. please help, my resentment is huge. I'm in therapy and my therapist says i have to set boundaries. My parents have more or less idicated that they want nothng to do with me if i dont do as they say and my dad, becaue shes been in for two weeks, has had a break and has just lashed out at me on the phone as i asked him how will he cope over the weekend if she kicks up and wants to go back into hospital. He said 'how the f should i know' really agressively. I'm so worried about them both. I love them and want whats best for them but i dont know am i able for the onslaught of pulling back but my life is in tatters as its not free of them. Can you give me some excuses, some 'illness' i could make up, just to 'pull back' for now as i'm exhausted.