Divorce

Hi, My Brother got married on Feb 3rd 2017, spent a good 1.5months with my Sister in law until his stay in India and had to go back to US for work, and while he was working on the visa for my sister in law on April 8th she goes to her mothers house(which is 30mins away) for a function and says shall never return as she isn't happy staying alone with my parents. 2days later we get to hear from her parents that she is absconding from their house, while their parents kept searching and filed an FIR it has been of no use till date. We get to hear from family and friends that she had an affair before the wedding with another married guy and is currently with him, we do not have any proofs though. Apparently she argued with her parents saying she doesn't want to go back to my parents house, as my brother is not keeping in touch enough and might be in a relationship. When their parents did not agree to this she decided to leave the house. its been 1.5months that she is missing, though she has called my brother 2-3times in this duration asking for divorce but her parents do not agree for the divorce and just delaying this by asking us to wait until she comes. The girl has always been mentioning to my brother that she is in touch with her father and has mentioned bout divorce but the father has never agreed the same when we ask. the father is a Public prosecure in a town in Orissa state. Kindly let us know what should be our action plan here. PS-Our intention is to sort this simply by a mutual divorce and not get into complications