Whether an agreement on paper holds any value wrt property

The self acquired property of my grand father is still in his name. He died a long time back in 1970s. My father has one brother and one sister. My father and his brother made a agreement as to who will reside on which side in the property and as my father got a larger area, he even paid some cash to his brother. This all was written on a plain paper in 1992 in presence of 3 people. My paternal aunt was not consulted and was ignored at that time. However, that document was not registered under Registration Act 1908 or any other act/rule. Now, my paternal aunt wants 1/3rd share in the property. I want to know whether that document holds any value and whether my paternal aunt can claim 1/3rd share and gift it to my father. I also want to know that if we file a case for claiming possession of a property which is presently in possession of our relatives, then the rent of that property will be deposited in escrow account maintained by court or not. And do we have to deposit any money (some %age of property/disputed property) in court for filing a case and if yes, how much and do respondents also have to deposit money in court or only the party who is filing the case needs to deposit money in court.