Domestic violence and dowry

Dear sir, its been 2 and half year to married my sister, at first her husband family has accepted what we are giving, after one month, her husband asked her jewellary as he was in need of money, she informed us and we said no, and after 2 months again he asked my sister he is in need of money, that is the 3rd month of their married life, and she was expecting, we gave him a cheque of 3 lakhs, and after sometimes he and his family started giving mental torture to her, but we asked her be patience, after birth of baby they will be changed, few months life was fine after 1st baby which was by seizure ( by operation) and even after two month we are surprised to know that she is again expecting and after check ups doctors said, her and baby life could be in danger, anyhow we consulted many doctors and many prayers she delivered her 2nd baby, within a two years 2 baby girls, every one hope that everything is going fine, after 3 months of 2nd baby she return back to susraal and become suspicious about her husband acts, he was coming late and keep his mobile locked, one day she success to unlock the mobile and read his whatsapp messages, some of the messages which he sent to girl friends, she found he has many girl friends, which he giving gifts, calling them, dirty chats with them, after few days he got idea that wife is reading his whatsapp messages, he deleting the chat history everyday, now we are worried, she wont like to stay with such cheating husband and got 2 babies. her husband family is also blaming her for not doing work, you should do this that etc, but we said this is happened in every house and she has to listen to them, after sometimes everything will be alright. after knowing about his affair, she is fed and she cant live with a guy who use to go to other women. please advise what we can do for her, we are the one who arranged her marriage and we are feeling guilty now to helpless. we want a fair justice for her and her kids.