Sister's 2nd marriage; Problem wth inlaw; A Bro's pray for advice

My Sister (25Y) is facing a problem with her 2nd marriage (1st marriage was a divorce under mutual consent) and the trouble arose due to her Mother in Law. The In laws were told very clearly about her 1st marriage & reasons for divorce before the 2nd marriage & the match was set by their relatives very well known to us from the past 30 yrs. Everything went good for the 1st 30 days after marriage and then the problem started. We were given to understand that she was asked by some of their relatives reasons for choosing a divorcee. She was able to justify them initially after which she was not able to and started harassing my sister for all trivial reasons. My brother in law who was very much lovable initially with my Sister turned up to a position that he started supporting his mother since he keep admiring her badly as she took much pain in bringing him up. His mother initially started blaming that my sister has some Doshams and they need to be rectified by prayers for an year. Later on she started blaming that she has not got enough money from home as dowry despite we fulfilled their wishes whatever agreed. Now its been 13 months since they got married and they were together only for the first 2 months. My inlaw left to his work place in Kerala and slowly started staying away from us and his wife as well. No we came to know that he has left abroad without informing us and when we contacted his parents, we were told that even they are not aware of his where abouts and he is not calling them at all which is a false statement. This everyone of us are aware since he is strongly connected to his Mother in such a way that he will not be without speaking to her atleast once a day. When we tried to ask what is their problem with the help of the ones who proposed the match at first, she started lying that my Sister is not doing works in home as per her desire (being an engineer and who was doing job till her marriage) and she also claimed that she came to know that my sister's behaviour is not good due to which her 1st marriage was divorced and this was told to her by the 1st in laws when contacted. Now through other sources we came to know that they have approached an advocate to separate under mutual consent for which we are not ready since we were already troubled once. Now there is no response to us directly or to the ones who proposed the match from the in laws and even my brother in law is not responding to our calls or mails being abroad. They ruined us by taking money from us, marrying my sister after knowing everything about her first problem, later harassing her, now propagating that she is bad due to which they want to separate and finally spoiling my sisters life and my parents health. Pls advice what decision / kind of action to be taken. At the outset we want my inlaw be with us since as a person he is good without the influence of his mother. Suitable advice will keep 3 humans happy throughout their lifetime. Thanks in advance.