Structure on setback being used towards commercial activity

Dear Sir In the apartment building that we reside in, an area of 5.3 meter has been marked as the front set back area in the Guwahati Municipal Development Authority approved drawing. Now the tenants of apartment Block 1A who runs a Café (A Bistro House) wants to encompass the front set back area by putting up structure towards carrying out their commercial activity. To the best of our knowledge Set backs are common areas and are kept free where no construction either temporary or permanent can come up. Do the tenants have the right to use the Set back area towards their commercial activity. Ours is a co-Operative society and the original owners of the land had already been allocated individual apartment etc as per their terms with the builder. Does the land original land owner have any exclusive right over the seback area?