Legality status and opinion

My name is kalyan. My great grand father is S.peddaNagappa who has 2 sons named 1)Rajappa 2)chamundi and 2 daughters named parvathamma and eramma. He had property of 180 acres n some houses in the year 1957 Peddanagappa along with his 2 sons had done a registered partition deed setting 60 acres each to three members. And He died on 1969 without leaving will. After his death in 1975 his daughter parvathamma and chandrashekarappa(s/o eramma) filed a suit for partition in civil court and they obtained a priliminary decree saying to appoint advocate commissioner and divide the land into three shares each 1 to rajappa 1 to chamundi and 1 to parvathamma and chandrashekarappa.But they didnt do so and didnt obtained final decree n all of them colluded and wrote a document saying that "peddanagappa wrote a will on 1975 to divide the property to 4 mems and also through the decree of court" they are dividing the property through a partition deed which is unregistered. But actually peddanagappa died on 1969 and in that document it is shown that he wrote a will on 1975. After that rajappa had 1 son named mallikarjunappa and daughter named eswaramma Chamundi got 1 son named bhaskar n 2 daughters. Rajappa wrote a will to mallikarjunappa as obsolute owner of his properties and he died .Now in 2017 i am son of mallikarjunappa when i checked the documents carefully i have found out that there was mistake in document and thus they are not entitled to share in property. I have recently seen chamundi's son bhaskar sold land by keeping link document as 1957 registered partition deed then i came to know that 1977document is false my father too knew it but because of many troubles he had not filed any suit towards this upto now. Now my question is 1-Is 1977 unregistered partition deed is valid showing a will dated 1975 when nagappa is no more and also showing priliminary decree of court? Or 1957 registered partition deed between peddanagappa and his sons is valid ? 2-can i claim property back now my age is 20 years 6mnths now ? If so how can i ? 3-They have been in possession these many years but with showing false documents and i know these now what can i do now ? 4-they have sold 20 acres of land to some others can i do anything for that ? 5-They are not cultivating land by themselves and that is agricultural land i am 20 years now what can i do now if they say they are in adverse possession ? What is the legal way to protect my interests in the property and justice and get back property?