What do you do when my nieces are verbally abused by a girl my sister took in who is homeless and pregneat?

My sister took in a girl.. One nightmare, after another with my sis. She has 5 children -has had problems with the health of 2 children which have been serious. Now, she has moved in (to my parents home where she stays, she and the 5 kids and the husband) a girl who is 16 or 18 not sure they keep lying about the girl and I only know her name to be ashley that she is pregneat and has a trucker mouth and my nieces complained the girl is cussing my nieces out. My parents are fighting my mom went to my grandfathers to stay. Dad stands behind my sister on letting the girl stay. I have called Child Protective Services on this but I don't know what else to do! I am worried for the saftey of my nieces and nephews! My sister and dad have no history on this girl and she carries on like a mad cow! What if she has her friends robb my fathers home or god knows what? I can't talk sense to my dad or sister. Someone Help--Indiana here!!