How to specify a property in Apartment Act

We are two brothers having 50% each share of our 10 Marla house in Chandigarh where Apartment Act is not available so it is not clearly specified which 50% is of whom. Although it is being considered that ground floor is 50% and first floor 30% and the top floor which is second floor is 20%. Now that I am leaving on first floor so I am considering my 50% as first floor and second floor and the ground floor is been occupied by my brother who is living there for the last 50 years. I want to sell my 50% she is in the shape of selling second floor and first floor respectively but my brother says that according to Apartment Act no area is been specified and I cannot sell the second floor. Although I have taken the pocession of 2nd floor through the rent controller of Chandigarh. Please suggest if there is any legal complication coming my way. thanks