specific performance suit claiming possession of land

i purchased agriculture land (part of land) in april2016 which is an ancestral property and after demise of the father the surviving mother is the title holder as per revenue records ( but has 2 sons & 3 daughters) , the seller (Mother and 5 children sold the land to me through a sale deed in which all are parties have signed and have received consideration through DD's which are mentioned in the sale deed). Now I am in possession of land and planted mango trees . Now a specific performance suit is filed in the district court by a third person claiming possession of the land & cancellation SD