Hello,
If the property was jointly owned by by your deceased father and if the property has been mutated in your mother's name she can divide the property as she wishes.
Now your brother has no right .
If your brother approaches the court he will get only 1/5th of the 50% of the whole property as all children including the wife have equal share in the father's portion of the property as he died intestate
If the property is still in the joint name of your mother and deceased father as mentioned earlier your brother can claim only 1/5 of the 50% of the whole property.
Advise your mom to make a decision and act accordingly.
The options are she can gift her part of the 50% equally between the two of you after getting NOC from both the sisters and divide the rest equally as well.