Validity of Property parcentage share agreement on a white paper

We had ancestor property of 0.75 cents, there is no parent document but we had patta chitta kisth receipt in my father name, there was a dispute between my father and other party from my village whos father had falsely created a sale deed document (in 1985) from old Village munsif who is from next village, who doesn't possesed the land or holding any title over the property, 1991 my father filed a title deed and lost for not proving the ownership of the property for not having parents document and not proving owner of the patta number and in the same judgement , opposite party also lost as his seller (Village munsif) doesnt have the proof of buying it from anybody. There wer no dispute till 1999 , during that period patta and chitta adangal everything was in my father's name, hence we had created a settlement deed in my name by my father, upon hearing the settlement, again that opposite party's son filed a title deed in 2000, while the case was pending till 2003, i involved and compromised the opposite party's and finalised the deal by Writing down 63% for me and 27% of the land for them by mentioning the Court case pending and O.S. Suit no. in front of Village people and Panchayat President of that year. after the agreement i made them to withdraw the pending court case. now the problem was, they somehow sold 10 cents by hiding EC and changed the patta into their name and sold the entire property along with that 10 cents to the third party on January 2013, as i was studying my PG in chennai i have come to know only after a month about the sale. My question is 1. Can i use that White paper signed agreement to get my share? 2.How many years it can be a valid document? is there any validity years? example 3 or 10 years? 3.I already had filed the court case with that agreement, but opposite lawyer filed a counter saying that i cannot claim my share, as my father lost the case in 1993 (where in the same judgement his party also not proved his title), my case should be rejected as per Order 7 Rule 11.