Daughters right in already partitioned land

Respected Experts, My father has one elder brother and two younger sisters. All were born before 1956. My grandfather expired in 1987 and his agricultural property was partitioned between my father and his brother in joint account with the consensus of my father’s sisters by submitting affidavit in front of Revenue Inspector in 1988. Since then my father has been cultivating the said land and in his possession. Again above said land was partitioned between my father and his brother into separate (which was in joint account) account equally in 2010. At present my father’s sisters claiming their share and filed a suit in the court. An affidavit which was submitted to the Revenue Inspector is with my father’s brother and refusing to give us. As far as evidence is concerned, two people had given witness on the affidavit. During partition process in 1988 we received a notice from Revenue Department regarding any objection, but nobody objected during partition process. Partition is not registered with sub registrar office. Property is located in Karnataka. 1. What kind of partition is this? 2. Is this kind of partition allowed or has value in the court of law right now? 3. Is there any chance to win if I continue to fight in the court of law against them in the above said circumstances? THANKS IN ADVANCE