your brother and his wife have crossed all limits of decency and hence you did the right thing by filing an FIR.
a suit should also be filed under the Maintenance and Welfare of Parents and Senior Citizens Act, 2007 which is a legislation enacted in 2007, to provide more effective provision for maintenance and welfare of parents and senior citizens. This Act makes it a legal obligation for children and heirs to provide maintenance to senior citizens and parents, by monthly allowance. This Act also provides a simple, speedy and inexpensive mechanism for the protection of life and property of the older persons.
A senior citizen including a parent who is unable to maintain himself from his own earning or out of the property owned by him is entitled to get relief under this Act. Children/grandchildren are under obligation to maintain his or her parent either father, mother or both. Likewise, a relative of a senior citizen is also bound to look after the senior citizen. If such children or relative is not maintaining his parents or senior citizen respectively, then the parents/senior citizen can seek the assistance of Tribunal constituted under this Act, to enforce the remedy of maintenance. Such parents/ senior citizen can file an application before the Tribunal, claiming maintenance and other reliefs from their children/relatives as the case may be.
Such application for maintenance can be filed by the senior citizen or a parent himself, or if such a person is incapable, then by any other person or any registered organization authorized by him. The Tribunal can also suo-motu take cognizance of the case. After receiving the application the Tribunal may issue a notice to the respondent-children/relative and provide them time to furnish their reply. Such application for maintenance should be disposed of within 90 days from the date of service of notice of the application to the respondent. However, the Tribunal can extend the time for a maximum period of 30 days in exceptional circumstances after recording reason. The Tribunal is having the power to allow interim maintenance pending disposal of the case. Even though the application can be filed against any of children/relative as the case may be, such respondent-children/relative can implead another person who is liable to pay maintenance.
If such children/relative who are directed to pay maintenance fail to comply with the order of tribunal without sufficient cause, the Tribunal may issue warrant for levying the due amount from them in the manner levying fines and can also sentence the erring respondent to imprisonment that may extend to one month or until payment made whichever is earlier. The Tribunal will not issue Warrant to execute the order of maintenance if such petition for execution is filed after a period of 3 months from the date on which the maintenance is due. The application under this Act can be filed before the Tribunal in any district, where the applicant resides or last resided or where children or relative resides. The evidence of proceedings shall be taken in the presence of children/relative against whom relief is sought and if such respondent is willfully avoiding service of summons or neglecting to attend the Tribunal, the Tribunal may proceed and determine the case ex parte.
your father being in the army does not come as a hindrance in filing the case.