Abusive Marriage, Mental Torture, 6 years daughter, rucks every 2 months, deprivation

My Sister married to a man in 2017, it's been 7 years but there marriage is always in hurdles, there are constants fights, verbal abuse, abuse her family(my mother and me), he always complained to her saying we didn't give them much in dowery, multiple times we have asked elders to come in between and settle their marriage but it's not happening, they fight on every peculiar reasons and then she travel to my home and stays, now i'm also fed up with this as this is keep happening, Most recently, her found out she is involved with some other man, and found photos in her phone, and kept her phone, she is crying, and asked me to book car for her so that she can travel to my home. We live in same city. I got a job in this city, but half my time goes in her life ruckas, which has nothing to do with me. I'm 11 months older than her, her husband now accusing us saying, we married her to him even after knowing she was involved in other man, right from the beginning. Moreover, we never interacted with her lover, although he is the same guy from hometown, with whom she had affair but back in 2015, he married to someone else, and then we found her current husband as potension match and she agreed to marry him, and after this long, same story is getting repeated, she is 27 years old now and i'm 28, single, taking care of parents in new city, but every 2 months, I have to go through this stressed situation in her life. We were/are not okay with her lover, because he's loser in life, don't have a job, drinks, chews gutka, ride rented auto rickshaws, married to other woman, have 2 children, total miserable man, but she seems all heels down to him. Now my sister and her husband has 6 years old daughter, I'm uncertain, what will be right solution of this problem once for all, her husband ask her to initiate divorce, and she is little hesitant to that, but keep on creating rucks which impacts my life. My mother and grandmother is super stressed about itself, i feel stuck in this very badle. I don't have father, I'm the only male earner in the family, mother and grandmother stays in my house in Pune, and now she also shifted to my house with her daughter, and there is constant phone abuse between these two, which hurts me. In all of this, She never blamed her lover for all of this mess, I don't know what she want in her life, she never opens up about her real intentions. I tried all the ways to talk to her regarding this, she is just too much into her other guy, I told her she can marry him/ run away with him but take some initiative but again not solid respond, just not now excuses. Please help me , and sorry for long post.