- Section 13B of Hindu Marriage Act, 1955 specifies divorce by Mutual Consent. Your brother and her wife can only file for divorce on ground of mutual consent if they have been living apart for 1 year or more. This is the basic requirement which is meant to be fulfilled while filing for divorce under Section 13B.
Since your brother and sister-in-law have not completed one year of their marriage, they cannot apply for divorce under this ground.
One thing must be very clear, living separately does not specifically mean that they have been living apart. Even if they have been living together in the same house yet not acting as husband and wife, they are said be living apart. When such period of one-year lapse, your brother can contest for divorce.
But he would only be able to file for divorce on ground of mutual consent if his wife is ready to do the same.
- Your brother can however file for divorce on ground of Cruelty mentioned under Section 13(1) (ia) of Hindu Marriage Act, 1955. It is not necessary that cruelty has to be in form of physical force, it could be mental too. It is the duty of a wife to live with her husband and if she denies to do the same, it would amount to Cruelty on her part.
- He cannot file for divorce on ground of Desertion as the minimum period mentioned under Section 13(1) (ib) of Hindu Marriage Act, 1955 for desertion should not be less than a continuous period of 2 years.
If your brother still wishes to live with his wife, he can file for Restitution of Conjugal Rights under Section 9 of Hindu Marriage Act, 1955 which states that when either husband or the wife has withdrawn themselves from the society of other, the aggrieved party can file for their Restitution of Conjugal Rights. If the court is satisfied with the facts of your case, it would order your sister-in-law to return back to her matrimonial house.