Divorce advice needed

Hi, my question is related with the marriage issues that my brother is facing in his marriage. It's been around 11 years when he got married and now he is blessed with a boy (will be turning 10 this year). My brother is very simple, or you can say that people take his simplicity in another way and consider him below average IQ case and he stammers also. However, when he got married my family spoke each bit of these details to my sister in law's father and then this marriage took place. Now its been 11 year to this marriage and there wasn't a single week where my parents didn't face mental issues because of her. This women doesn't like my brother and doesn't talk to him like what a partner does. Now, its been like 6 months when we got to know that she is trying to get involve with other men. Now, my family especially my mom is really upset and disturbed. She doesn’t sleep properly. Please suggest me how we can take this ahead in legal way. We are concerned for my nephew also and don't want her to take him with her. She is staying with us because she has a mind set that after my parents the whole wealth will be hers only and that's the reason she is staying with us and we are afraid that because of this she wont give divorce to my brother. My brother is only 8th pass, and my parents are not well aware with the world and that's the reason my taking a step and posting this query. Please help me