Impleding (Mother and Brother)

My relationship with my wife got estranged due to reasons more than one and thereafter she has filed cases for maintenance under DV Act at the CJM court and got the house owned by my father attached by The Family Court by providing false claims to the court that she had handed over 125 sovereigns of gold to me after the marriage. Recently my father passed away and now they have initiated a suit to implead my mother and brother as the legal heirs of my father in the Family Court case, inspite of the fact that there is no case that was put up against my mother and brother. The objection in the Family Court was filed and the same is due for hearing on Jan 4,2017. Now my mother and brother has received a notice from the court asking for their appearance before the court on Jan 4. Qtn-Should they attend court on Jan 4 or what should be done at this stage? Qtn-Is it a procedural error to summon parties, who are not parties in any former cases and that too before they are impleaded? What should be done so as to lift the attachment in a property which has been purchased by my parents? Regards Sajan