Hello, im 15 years old

Hello, im 15 years old. Im in high school, and I have a 21 year old sister. Recently she was releaced from the Army, and got tangled up with a young man by the name of Jason. This man has a 2 years old son, and has gone through many girlfriends which are REALLY scared to break up with him. One of these people happen to be my sister at the moment. Her best friend contacted my family and said that Jason has been mentally and physicaly abusing her. Which includes biting her ankles, and stomach, etc....I was wondering if a physic could help me and my family find out weather her will harm his 2 year old son, and if it is true he has tried to kill people!! PLEASE help my family and i figure this out!! Thanks!!