Why does my famliy treat me so bad?

There are always people like this in the world who are not sincere and talk badly about you for no reason. The Step sister is probably directly from the Step Dad so they will side together. Your mom says do not say anything because she is worried the family will break apart. I would suggest you do speak up to your step dad and tell him the truth, that you do not teach bad words, you do teach her how to eat, and you do feed her and potty train her. Just have a talk with him if you get the chance and your sly step sister is not around. And don't let them accuse you learn to speak up for yourself in this world. Don't worry if you are a girl, don't be shy. Have you heard Beyonce's song "who run the world girls"