1. You have stated that the property stood in the name of your deceased father who died intestate,
2, You can collect the certified copy of the title deed from the office of the Registrar,
3. After the demise of your father, all his legal heirs i.e. all his children and wife, have become joint owners of the said property with equal share,
4. So, all the legal heirs, including your mother, will own 1/4th of the said property,
5. Your mother has no legal authority to disown or disentitle your younegr brother from his share of your father's property,
6. She can disown him to acquire her share of the property only,
7. If your mother and siste executes and registers Relinquishment Deed relinquishment of their shares of the property of your father, you get 3/4th of the said property and 1/4th share is still retained by your brother,
8. So, you can not sell the entire house to a third party without the consent of your brother.