If the property was divided floor wise and was bequeathed to both accordingly then you cannot dispute or object to the sale of property by your brother.
However though floor wise partition was mentioned in the Will, you still have rights in the land underneath the structure equally.
Therefore your brother can sell only his share in land and the ground floor structure to the prospective buyer.
Legally you cannot object to the sale nor you can get a stay order.
However if there arises a commercial establishment in the residential property, you can object it and give a complaint to the local civic body about it, if no fruitful result is seen then you can file an permanent injunction suit against the buyer.