Validity of settlement deed for undivided property

Property was bought by my great grandfather in 1941. He had sold 1/3rd undivided share of the property to two of his grandsons (my father and his younger brother) via sale deed in 1961. My grandmother is the only child to my great grandfather. Including my father, my grandmother has 4 sons. Upon my great grandfather's death, my grandmother enjoyed the 2/3rd undivided share of the property. Both my father (his share ie half of 1/3rd undivided) and my grandmother (half of her 2/3rd undivided) together made a settlement deed to my favor in 1992 (totaling 1/2 undivided share). Post the settlement deed, my grandmother continued to enjoy 1/3rd undivided share and my uncle enjoyed 1/6th undivided share. My grandmother and father died in 1994 and 2007 respectively. Property is still not partitioned. Pls advice whether settlement deed is valid, if my siblings challenge it in court.