Informing the father about the husband's immorality

Q: I have a sister who wears Niqab (face veil), offers Salah (Prayer), observes Sawm (Fast), and fears Allah (although none can verify this but Allah). She is married and has three sons and two daughters. She has been married for fifteen years to a husband who does not offer Salah except in Ramadan or on some other occasions. He also delays taking a Ghusl (ritual bath following major ritual impurity) for two or three days. Moreover, he does not offer the Jum`ah (Friday) Prayer or takes a Ghusl for it. He does not even pay Zakah (obligatory charity) due on his wealth and he deals with Riba (usury/interest)-based banks. Furthermore, he accompanies friends who are well known for their unsavory characters. He travels to Arab and European countries, known for dissoluteness and libertinism, for the purpose of having fun and entertainment. Sometimes, my sister, his wife, hears him while he is talking to his bad friends about his adventures while traveling in indecent words that cannot be quoted. He loves free mixing with the female sex and is a womanizer. Recently, he has come to be a friend of a religious scholar who has started to advise him, made Jannah (Paradise) desirous to him, and warned him severely against Allah's punishment. Thus, he has started to offer Salah and take a Ghusl, but he still refuses to pay Zakah and deals with Riba-based banks. Moreover, if he mixes with women in a party or wedding he gets lost and indulges in talking and kidding around with the women. Your Eminence Shaykh, my sister spares no effort to advise her husband, (Part No. 19; Page No. 393) but she does not tell her father about the husband's true character, so that the father would not seek to divorce her. The husband, on the other hand, cares neither about his wife nor about his children.1- Is my sister sinful for not telling her father about her husband's conduct and the reality about him?2- Is my sister sinful for being provided for - along with her children - through money that is acquired from Riba-based banks?3- What should the wife do if her husband abandons Salah again and deviates from the right path? Is it permissible for her to go on in her life with him as such to provide the children with a valid family environment?Please answer us, may Allah bless you. May Allah reward you well for serving Islam and Muslims.