brother in law filed a divorce notice & and is evading meetings.

hi, my sister and brother in law have been married for 2 years. For first 1 1/2 years all was fine but later my sister's in laws started living with them. She started struggling to meet their expectations which led to frequent altercations, her husband always sided the his parents. My sister was left to tears practically everyday for some shortfall or the other. So my parents visited her and on a very cold welcome from her in laws and looking at her fragile mental and physical state decided to take her home for a week so that she regains some semblance of balance. On reaching her home she made calls to her husband who blocked her number, myself and my parents repeatedly tried reaching my brother in and his parents but they don't pick our calls. I went to meet them but they did'nt open door. Now finally a few days back we have received a legal notice for separation u/s 13 b else they will initiate under 13 ia. We still believe the difference are petty issues and the marriage can be saved but for that we need to talk, we used various channels of friends and relatives to get them to talk, but all in vain. Do you have any suggestions? There was never a angle of dowry here as we provided whatever they asked for infact my brother in law is in possession of almost 680 grms of gold among other things. Not able to figure out what he wants and he is not talking, dont want to make things big time legal as that may lead to a point of no return. Thanks