should I confront my mom? Acs? evil? step dad? step sis? life?

Haven't spoken to my stepsister in a few years, (maybe like 2) yesterday she reached out to me and I invited her over, I personally thought she was staying away because she doesn't have the best relationship with her dad. Come to find out she tells me my mom called her and accused her of calling Acs on my mom... my mom said "you're a bitch I always knew you wanted to break up my happy family" (which is not so happy to me) so a little while after that her dad called her and said "you're dead to me for doing something like that" and hung up on her... and she says she haven't spoken to them since(even though she tried) but she was hurt that they would accuse her of doing that and there's our little siblings involved and that's why she's been away. meanwhile I'm just thinking she's choosing to stay away when all along it was my mom who caused all of this drama and all of the times I've been around my mom she never mentioned any of this, meanwhile my mom and I don't have the best relationship but I personally feel like she was wrong and my stepfather is even more wrong for taking his wife's side over his own daughter, my mom even went as low as to ask if I called them! I love my siblings to pieces even though my stepsister and I can agree that our parents aren't the best...that's some shit we would never do because our siblings could have been taken away!  but when Acs is called on you, from my knowledge they don't tell you who called but to accuse your own stepchild is low. my question is should I confront my mom? I'm personally tired of fake shit and my family living a lie or should I just move on and continue building my relationship back with my stepsister ?