Rights of Illegitimate Child over ancestral property

1. My father bought a property from his uncle 30 years back 2. His uncle's mother (My father's grandmother too) wrote a will as this property goes to his (Father’s uncle) children’s and in the meantime he can utilize/operate the property. 3. And she also mentioned that “My Son has a Mistress and children’s through her possess no rights on our property and our property solely goes to our grandchildren’s through the women we selected and get married to him.” 4. And the will also states, “My son and Daughter in law is also residing with us now in plot 123, Gandhi street." but she didn’t mentioned the name of her daughter in law. 5. Here come our issue, my dad got the property solely with the agreement of his uncle his son and daughter through a legal wife and acquired the property legally with all dues. 6. in the mid years of 2000. We are dragged into the court by the sons of my father's uncle's mistress stating that they're the legal heirs and we possess he property with the agreement