OP, I'm another one that thinks that you don't know what you are talking about. I have cut out my sister and parents (and thus the rest of my family) because of their crappy, crappy treatment of me.
My sister and I have never had a close relationship because of the sibling rivalry instituted in my family by my grandmother and mother. As teens my sister would openly ignore me in public and we never spoke to each other during school hours.
In my mid-twenties, I was overseas for two years after finishing university. When I returned, I found that my mother and sister had conveniently bundled up all the family's problems and scapegoated/blamed me to 2 of my cousins in my absence. I wasn't even there to defend myself. And of course nothing was said on my return, I only found out about this a year or so later. Needless to say, my sister 'apologised', but effectively said she was going to do nothing to fix the damaged relationship between me and my cousins. That was when I realised that I did not need such an uncaring and unremorseful person in my life.
My mother is a completely nutter I have realised recently, but she is very good at 'appearing' normal. You only have to scratch the surface a little to realise that she is completely nuts. FFS, she and my father believe that "food and money are love", they even said this to me a little while ago. No they are not, only love is love, and no amount of food and money can replace that. After a lifetime of her lies, manipulation, backstabbing, triangulation, lack of love, gaslighting, neglect, lack of guidance etc etc, I have decided that there is nothing positive that she (and my father) bring to this relationship and I have cut them off. I thought about it for a several months before deciding to do this and felt enormous (but misplaced) guilt, which I am now training myself out of.
As some other have said, there was a final straw that broke the camels back. Just before I decided on NC, I had been putting in small boundaries with her, such as "please don't ask me when I am going to go to bed every time I am here, I am a adult who can decide for myself when I go to bed". Her reply was "But I ask your father that question and its ok with him (!)" FFS, although my father and I are very alike, she cannot see that we are 2 different people! She complained that I was 'disrespecting' her, and had a complete strop at me, shouting at me until I broke down in tears. I have not seen her since.
A few months ago my father got her to apologise, but it is in the vein of those apologies that other posters have talked about. She said she "was sorry that we fought", not that she was sorry that she shouted at and upset me. A huge difference - she is absolving herself of any responsibility and effectively still thinks that she is in the right. I have ignored any attempts from them to get in contact with me. The last letter from my father said "this is a small thing that should have been forgiven and forgotten about." In other words, "Suck it up sunshine, we should be able to treat you this way and you should take it because you are our daughter. You have no right to expect any other sort of treatment".
I know that I am a product of mental illness on both sides of the family, and effectively I am the black sheep because I am a rational and psychologically normal person. I can see narcissism in my maternal grandmother, mother and sister, and to a lesser extent in an aunt and her 2 daughters. My father has schizoid personality disorder due to the schizophrenic mother that he grew up with. Three of the women in my father's side of my family committed suicide, probably due to the lack of care and neglect they received as they were growing up. The last one to commit suicide was several years ago, my father's sister (my aunt) who was only 4-5 years older than me, and who I used to play with as a child. At the time, she left a devastated man who loved her dearly and an 18 month old baby. The only way I can protect myself from this level of emotional abuse from people who cannot see what they are doing, is to have no contact with them. I will not be judged as cruel by someone as you, who clearly has no idea. I would give anything to have you subjected to 45 years of emotional abuse from mentally ill individuals, and not come to the same conclusions I have. As they say, walk a mile in my shoes...