Is it possible for my father to leave his entire property to me and my sister in his will, without telling my mother? My mother has her own home, but she plans to give it to someone else, so she wouldn’t be left with anything.

Yes, your father can legally leave his entire property to you and your sister in his will. However, under the Hindu Succession Act, your mother is entitled to a share of his property, and this cannot be excluded by the will. She can challenge the will in court, and may be entitled to a portion of your father’s property.