I don't know how to help my mother and sister

I have a 12 years old sister who goes through her character development phase. My mom is quite conservative and she does not agree with lgbt, all black clothes and all those things. Thing is, she has a huge ego, doesn't take any advice and keeps yelling at my sister things like "DO YOU HATE ME?? WHAT DO YOU WANT FROM MY LIFE? YOU SHOULD BE ASHAMED". I tried talking to her for so long telling her yelling is not the best solution and she should try other methods, I told her she should not take her anger out on my sister, that my sister doesn't need to hear such things from her. But she never listens and takes it all personally saying that we keep criticising her, we accuse her, she's only good at making food for us, victim mentality. My sister, of course, is very deeply impacted by this, she cries and comes to me and tells me that she just wants a mother who hears her feelings. My mom continuously yells at her and was like that to me as well, i have a deep self hatred and low self esteem now in my 20s, I'm very shy and can barely talk to people. I don't want my sisters self esteem to be impacted like that but apparently it is, she doesn't like anything about herself as well and even though I keep telling her she's beautiful, she doesn't seem to believe it. Mind you that my sister is also difficult, she has a strong violent character, anger bursts, but I believe this is all because she feels misunderstood. Im thinking of gathering both her and my sister and let them have a talk, while I interfere too, asking them what are the things that bother each other and try to find solutions. But I don't know if its the best idea. I told my mom to read some books on parenting or go to a therapist but she was deeply offended. Any advice? via /r/Parenting https://ift.tt/3sxiY48