Under the Maintenance and Welfare of Parents & Senior Citizens Act, 2007, a case can be filed by you if your parents authorize you. Under this Act, the Court can be asked to pass order to protect the senior citizend. Unfortunately, here again the case will be filed against the chidren, i.e. your brother and not agaisn the daughter-in-law. The other option is that your mother can file a suit for Protection Order against her daughter-in-law under the Protection of Women from Domestic Violence, 2005. Under this act, the case can be filed only by a woman who has a domestic relationship with the accused. Therefore, only your mother can file a suit against her daughter-in-law but your father cannot employ this law. He will have to file a FIR agaisnt his dauhter-in-law.
It is generally accepted that the woman centric laws have been misused extensively but you cannot simply lose faith in the judicial process. Even if your sister-in-law files a case under the numerous laws protecting women, it is not possible to be successful in these claims without strong evidence. If your brother and parents have not treated her inappropriately in any manner then there is no possibility that your brother will be charged with these offences. Similarly, if you intend to file a FIR or a case agaisnt your sister-in-law you will require substantial evidences to establish your claim. It is therefore advised that your parents must procure evidences whcih can prove that they are being illtreated at home by their daughter-in-law.