Nature of ancestral property is very unique. Only coparceners have interest in the ancestral property no other person such as mother can claim therein. Mother does not become owner of the ancestral property after the death of her husband. But children of the deceased father become the owner of the ancestral property. Your sister, younger brother and you are the owner of that ancestral property.
Also read: Daughter’s right in ancestral property
Ten acres of land and a house are self acquired property of your father. His wife and children are entitled to get share in that property. Your mother has one fourth share in the house and same share in ten acres of land. She can give two and half acres of land and ¼ area of house to her younger son through a gift or testamentary will. If all the legal heirs agree to settle the property amicably then prepare a registered settlement deed. Get it registered and mutate your name in the land records.
File a civil suit for division of ancestral and self acquired property
If there is no chance that they will be ready for a the amicable settlement then you should file a civil suit for the partition of property. Try to keep only one legal heir as a plaintiff and make the rest of them as defendants. Because if there is only one plaintiff then he will pay less court fees. Your sister is necessary party but she does not want share in the property so you can frame her as a proforma defendant.
Also read: Gift of ancestral property
Get relinquishment deed from your sister
Your sister does not want her share in property. So you should take a relinquishment deed from her. She can prepare a relinquishment deed and register it in the Indian Consulate of USA. The relinquishment deed that she is relinquishing or giving up interest in the ancestral and self acquired property of her father. That deed will be admissible in evidence. You should produce that relinquishment deed along with the plaint. Thereafter the court will not ask to make her a party in the suit. Thus you can divide the ancestral and self acquired property among the siblings and your mother.
File a suit for cancellation of gift deed or Will
Move a civil suit for cancellation of deed if your mother has prepared any gift deed or a testamentary will in favour of your younger brother. Your mother has no right to alienate all the property to her younger son. Therefore, if she has prepared any deed or will it will be void. So, you should take steps to nullify that deed or will in the lifetime of your mother.