Future of wife & children

Hi First of all, i want to thanks to create such a platform to get legal advice from expertise to people such like me who hesitate to go for legal advice . I want legal advice on my sister matter . she is 35y(MUSLIM) and got arranged married around 10year ago to a UP police sub-inspector ,having two kids ( boy & Girl). she have been suffering domestic violence since than. last year i recuse him and brought back with her to my home after her husband badly beat him( broke his hand and mouth injuries )and lock her in room , since than she is leaving with her children at my home. now he threaten to divorce her on phone and to get married to someone.It is very easy for muslim men to say thrice a word and get free from all responsibilities towards his wife & children. i want to know what should we do ? 1):What is the future of children ? Are they entitle any right in his property .? Any maintenance for education and leaving ? 2) He is serving in utter pradesh police ,is there any provision in service act to give maintenance to his wife & children . please provide legal advice to me . Thanks & Regards Ammar Khan