@Scarlett1616,
The first thing you need to do is to talk to him - and let him know that his behaviour is not acceptable.
Do you and your sister live independently or are you still in your family home with parent/s? If your parent/s are in the home, you need to speak to them. They need to know what kind of people are in their home.
After speaking to him and any adults in the house, you can decide what your sister needs to know and how you are going to tell her. She'll be unhappy, but she will survive.