SELF Acquired property elgibility

Hi, Property was belongs to joined account of my father and mother , My mother expired 6 years back and my Father expired a month ago .Only we two of them ( Myself and My brother ) are son for my parents. My Father under gone 2nd marriage ( 2 lady age is 33 years )after a month of my mother death nearly 5 years back . The property of house has been build on my age of 13 years. My father written a document as he gifted 100 % of his belonging ( Means 50 % over all property) to 2 lady . . Little brief on the 2 lady as she was already married a person and she not get divorce properly from court . only they took written agreement in police station before marring my father. and my father is a policeman he also influenced. Now my question 1. as the property is build after my 13 years . Is it possible, my father can do 50 % property to that 2nd lady. or in that 50 % any possibilities for us to have contribution or my father not taken clearance from our end also while gifting to 2 lady.. 2. As the 2 nd marriage is illegal , so what my father given gift to that 2 lady is valid or not.