I know it's hard since you are younger, but if she had been my sister, she would only hit my dog once. And, with the way your dad is, it'll be hard talking to your parents about it. Maybe that's where your sister learned her behavior? Just try to be nice but firm about it an explain that hitting your animals will not be tolerated. I would keep them with me as much as possible. I feel sorry for any living thing your sister gets as she's more than likely not going to truly love them.