Litigation of our registered property as their hirarchial one.

Dear sir, My grandfather (mother's father) has two daughters and no sons. He registered 2 acres of agri land (1acre for each) to Both of them, and kept 1acre land registered in his name still. His elder daughter is my mother(alive) and his older daughter expired before him. He made a will(unregistered) before his death clearly mentioning that the 1 acre land which is in his name should belong to my mother. He passed away in 1994 at my mother's residence. Till then the said 1+1 acres of land is in our possession and mutated in revenue records and we got passbook, title deed in my mother's name. But we recently found that the survey no.s of the said property is wrongly entered in revenue records differs from registration documents. Now, my mother's brother in law (expired sister's husband) litigated this property by using the mistake of revenue records (he used correct survey no.s which are in documents) as they got it from his wife. He also registerd 1.5acres of land to his daughters without our consent and tries to grab our land by forcing us to agree for settlement. I think he influenced revenue officials too. When we request to correct the revenue records, the officials suggesting us to go for settlement. We still have control on the 2acres land, bank loan, paying taxes, adangal, encumbrance, etc.. But with wrong suvey no.s. We applied for the surveyor, and MRO and the matter looks unmoved. Please help me what to do and what not. Thank you.