Heirs of previous owner claim ownership to agricultural land after three successive transfers

Person A (male) sold an agricultural land to person B in Year 2000. The sale deed was duly registered. B sold the same land 6 months after (i.e. in Yr 2000 itself) to four persons C,D,E and F. The sale deed was duly registered. Persons C,D,E and F sold the same land to person G in year 2005. Again, the sale deed was duly registered. Later on, the land was acquired (compulsory acquisition) by the government and part compensation was paid by the government to person G in yr 2016. Person G died in 2017. Subsequently, person G's three legal heirs (widow, son and daughter) added their names to the 7/12 document. A few months later, in the same year (2017), the 7/12 document was updated with the name of the government agency who acquired the land. However in the meantime, i.e. after the death of person G in 2017 and before the three legal heirs of person G had their names added to the 7/12, three sisters of person A filed an RCS petition in the Taluka Court saying that their brother i.e. person A had sold the land to person B without their permission. They say that the 7/12 document back then had only their brother's name on it, so he took undue advantage of the situation and sold the land to person B. They have prayed to the Court that the three duly registered sale deeds should be declared invalid/void/cancelled. The suit was brought after 17 years since the first transfer was made. it seems like a collusion on part of person A and his three sisters. What legal remedy is available for the three legal heirs of person G?