Registration of property without knowledge

Hi This is nayana from bangalore, I need help from you guys. My grandfather made some properties in the native and My mum is the only daughter to my grandfather and he passed away 20 years back. Now one of mum cousin ( my auncle mum cusin brother ) register the property from her without knowleding and also he bribe the sub register to not to read what is there in the paper and letter. And the letter continues . He only help financially to my mum to construct the house. . He made financial help to me and my sisters marriage . He is paying some money to register the property to his name at the time of registration. No one explain her these point and the details while registration and also my mum not educated and she doesn't know writing and reading. My request is what we can do in this case. Can my mum g file a case against to my uncle and sub register officer? If yes What are the documents required to file case? Please help me out my mum don't have concerns of property she has concerned on letter which they took signature without doing that because marriage, build a house everything my father did his own earn money. Please suggest me what we can do? Thanks Nayana