False signatures taken what to do

we have a property of my grand father "sister , we dont have any papers,but few yrs back some agents came and take my mother sighn(thumb) and given 20000 rs to her & recently my grand mother raise complaint againts my mother & brokers in mro officeshe is legal heir of that property, mro people call my mother &them to their ofice what should my mother wil do actually the broker didnot tell the property value and details plz suggest what should my mother wil tel in mro office plz advice me