Signatures taken by fraud on property papers 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 office she 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 to my mother,plz suggest what should my mother wil tel in mro office plz advice me, how can we prove the peoplewere fradly taken my mother sighn, no one is avaible with my mom that time plz suggest me , my mother was afraid of that , my grand mother was not supporting us