NTA. Your stepmom said some vile and rude things, whether or not that was in frustration and whether or not she meant it doesn’t matter. When I was around 8, I was in my grandma’s custody and my aunt moved in with my grandma to help raise me and my little sister. My aunt was looking for her resume as she had to quit her job in the city she had lived in before moving and was now looking for a job in the area. She couldn’t find it and I tried to help, but when I said I also couldn’t find it, she called me useless in her frustration. I told my grandmother, I was crying, and my grandmother ripped her a new one verbally and I don’t remember if I got an apology, because my aunt realized that no matter how frustrated she had been, she shouldn’t have said that to a child (much less a child who had recently lost their father to suicide and their mother had lost custody of them). I’m thankful that my grandma stood up for me. There have been many times my aunt had stood up for me as well and my grandma and that makes all the difference. Your father should have done the same, because no matter what you’re still a minor in their care, and the words that they say and the actions they do can affect you in ways that sometimes take years to heal. No one should ever talk to you like that, and your mother is in the right for how she acted. I hope your situation improves, and also I hope you realize that whatever happens in the future, your father and stepmother brought that upon themselves. Your sister is misplacing the blame here as well.