Partition of Property

Respected Sir/Mam, There is partition done of property between two brothers, as per the agreement both came under the consideration and understanding that, will divide the property equally and one side x will keep and another side y will keep and whatever falling on there side will belong to them. And there would no be any demand from any brother for a particular room or anything other which is not getting and another one is getting because it is galling under his part. And both brother x and brother y agreed on the part. but now brother Y raised the issue that there is a room which is falling under brother x part and he (brother Y) wants the money for that particular room according to current valuation and he (Brother Y) claimed that, a room which falling under brother X side cost of make is 95000 Indian rupees which is way much higher to the current value as per market. And brother Y even made an agreement with handwritten notes on 2 rupees stamp paper and by misleading and misguiding and giving threatening messages, he (Bother Y) made forcibly signed by brother X on that 2 rupees stamp paper, which is even not notarized by any gazetted layer or advocate. So, now I am the son of brother X and want justice to this, I request you to help me out and by referring above paragraph help me with solution, as again my question is that stamp paper to which brother Y made signed by brother X for agreeing to pay Ninty five thousand Indian rupees, would be valid if it is even not notarized or registered, and as I can get a fair chance to get the current market value of that room and I can again negotiate the value with brother Y.