First of all, thank you @chimain and @kaz so much for your compassion and thoughts.
About the LEAP method, they find it patronising when I have brought it up. Instead they try to reason/debate with my sister when she is sharing her delusions which results in a lot of tension and back and forth.
And @kaz yeah about the length of time - in 2018, I first noticed she was exhibiting unusual behaviour and after her pulling a knife on me, I was adamant that we needed to get her sectioned. My parents felt too ashamed to report it and told me that sectioning her would ruin her life. They told me to back off.
What has followed has been 6 years of me trying to call professionals and seek assistance, only to be told I am not her guardian and cannot do much. Eventually I persuaded my parents to seek professional guidance instead of basically handling it on their own. Finally they agreed.
Last year, before a family christening, she was in full blown psychosis. She had not been diagnosed or sectioned by then, but her behaviour was terrifying and I basically urged that we call someone immediately. My parents refused, as they did not want her being sectioned on the day of a family event, and brought her along to the christening. So we now know that because my parents overrode my decision, they took a schizophrenic IN psychosis to a christening.
A few weeks later, she nearly died. She was saved because I urged my family to bring her to A&E, where they sectioned her for 6 months and diagnosed her with schizophrenia.
What I am saying here is that whilst I understand a lot of parents or caregivers provide all the main care for their ill loved one, I really feel like I have made crucial decisions that have/could have led to the best care. I know we cannot expect caregiving to be perfect, or to be hard on ourselves, but I struggle to let go when I know I have played such a central role. Especially in the crisis stage.
I really want to back away, but considering she also has type 1 diabetes, I really am so scared that she will die. 