harassment

hi i really want help from you regarding my family okay.. as the past history my mom n dad are married for 2 decades! my mom adjusted with his family for 14-15years! as there is no support was given by his family. my father had flings and many other sexual contact with his colleagues, which i have proves of like (adult chat , photos of him) recently too. where I talked him about it and he accepted and let it go. we are two daughters and my father has not given us financial support most of the times because of which my mother got involved with a guy since 6years and he has given mental and financial support both! now my father came to know about my mom's affair( in which he has seen chats and photos with that guy with "no" adultery ) for which he is harassing my mom mentally that she has got syncopal attack because of lot of stress. he threatens us that he will commit suicide or kill that guy. he has even threatend by saying he'll make that guy in prison for 20-25years for adultery and we as daughters are being harassed by him badly. i'm not able to concentrate over my studies. so i want to know is there any prisonment for the act or any can he file any case against it? and how can we stop him by harassing us?