If all other legal heirs had relinquished their rights in the property in favor of your mother by executing a registered release deed, then ever since the execution of the registered release deed in her favor, your mother becomes the absolute owner of the property.
In that case she is the authority over the entire property.
If she had given the property to you by a registered settlement or gift deed, this decision cannot be challenged by anyone for any reason neither anyone can claim any share in that property as a right.
You can ask your brother to approach court of law for desired reliefs.
2. Your mother is the absolute owner of the entire property provided the other cosharers have executed a registered release deed relinquishing their rights in your mother's favor.
3. Yes.
4. If your mother is a legal owner and if the contents of the first answer above has been properly complied, you can sell your share of property that had been settled to you by your mother in your favor.
5. If your mother's title to the property is ascertained she can proceed without the consent of her children.