Fake Registry by means of submitting wrong documents

Dear sir. I shamsher singh adopted son of sh. Hawa Singh Vpo -Kuloth Kalan Tehsil-Chirawa Distt-Jhunjhunu Rajasthan 333033 My grandna ( nana ji ) has adopted me for his look after as he did not have any male child , had only 2 Female child( my mother & mosi ). After death of my nana ji and nani ji ,my grandna `family (His brothers ) is challenging and want to keep me out of my nana ji total share in land of His father i.e. 1/3 of total as they are 3 Brothers and 4 Sisters . they want to make it 1/7 Of total share so that my share will reduce to 1/7 In place of my original share 1/3 by means of placing fake documets/ fake signed summons isued by court. however i am having GODNAMA( SON ADOPTION COURT PAPER ) At the time when my Grandna was alive and all docs like voter id, Adhaar card, Tenth certificate in name of grandna ji and on his address. Pls suggest me for this issue how to handle. and how can i raise FIR or court case to solve this issue. i shall appreciate your response. thanks and regards. Shamsher Singh 8750031605