Query regarding Land on my late father's name

Hello sir/madam Good morning. My self Ramesh and i have a below mentioned problem. My father died 10 years ago and he has 4 acres land on his name. I have my mother, unmarried younger sister and married younger brother. My sister's age is about 40 years and she is not marrying for her silly personal reasons and now she is planning to marry any one who is not capable to protect and maintain her but she is asking 2 acres from my father's land as a dowry. My mother changed her mind by each others words and planning to sell some of my father's land. Can my mother sell the land on my father's name without our decision or signature legally ? Please advice on this issue for us. Thanks in advance.