Will my sister’s future be happy?

It has been more than 3 years now of sister’s marriage. Our parents both passed away before our marriage. My sister and brother-in-law, both of them are working and have a male child (2.5 years). My brother-in-law has drinking problem (even before marriage) and does not respect my sister and also has a habit of using filthy words against my sister. He has no religious knowledge and does not pray salah even on Fridays. Her in-laws are careless, money-minded and always use to find faults with my sister. Though my sister has gone so much trouble with her married life, she had hope that he will quit this drinking habit and someday can lead a normal life. She even admitted him to a rehabilitation center for 20 days and went through treatment. But he again came drinking very next day. She is being more tested managing her husband and child and work. She has become weak, restless, worried and the child is scared of his father. We are not sure how to proceed further. Request you to advise us.