Claim on property by adopted sister

Our father, in his first marriage, adopted an abandoned girl child. She was married off and is signed witness on his will where he has written her out of any claim on property. Father's first wife died after marriage and he remarried. As he had given away all pertinent gifts etc, he wrote a will nearing his death, naming everything to his current wife and two sons. This is the will that his adopted daughter is witness to. This property was then sold off to a builder and apartments were made. Now upon the death of his second wife/our mother, the adopted sister and her two sons are claiming right over property and claiming stree dhan. Their basis for claim is the initial purchase document of property in the first wife's name. This property was duly registered later in our mother's name. And then later sold to the builder. Nevertheless, They are using the initial 40 year old document as proof of claim. The Apartments have been sold on bank loans even. How valid is the claim?