How to reclaim ancestral property and proceed with selling it?

My mother is my father's second wife, married as per Hindu rituals, and is his only officially recognized spouse according to government records. My father is a retired Central Government employee. His first wife has a son who is not my father’s biological child but is currently residing with her in my father’s ancestral property. This property, originally owned by my father's great-grandfather, is now divided between my father and his elder brother. All properties bought by my father are in my mother's name. I also have a married sister. Now, my father wants to sell the ancestral property, which is currently under the control of the first wife's son. Queries: • Does the son of the first wife (not biologically related to my father) have any legal right to my father's property? • What legal actions can we take to reclaim the property and proceed with the sale?