@ Suchitra, Pl. see sec. 2(q) of the DV Act:
(q) "respondent" means any adult male person who is, or has been, in a domestic relationship with the aggrieved person and against whom the aggrieved person has sought any relief under this Act:
Provided that an aggrieved wife or female living in a relationship in the nature of marriage may also file a complaint against the relative of the husband or the male partner;
So in the case you mentioned you had in your office, there is no bar for the mother in law to be added as a party as per Sec. 2(q).
Learned friends, pl correct me if I am wrong. Thank You.