If you are telling the truth, then you need to tell your dad, so that he can do something to protect you, and your sister, and if he will not listen talk with a school counsler, also both you and your sister should go together one more time and tell mom, and tell her it is the truth, and that if he beats you again you will call the police, This is no time to be shy, also ask MOM why she is treating you this wayIf this man hits you hard enough you will get the courage to tell someone luck jo