The Landlord can not discriminate against you for having a family member live with you. The law is based more on the square footage of the apartment.
"HOUSING MAINTENANCE CODE Sec. [D26-33.03] 27-2075 Maximum permitted occupancy
a. No dwelling unit shall be occupied by a greater number of persons than is permitted by this section.
(1) Every person occupying an apartment in a Class A or Class B multiple dwelling or in a tenant-occupied apartment in a one- or two-family dwelling shall have a liveable area of not less than 80 square feet. The maximum number of persons who may occupy any such apartment shall be determined by dividing the total liveable floor area of the apartment by 80 square feet. For every two persons who may lawfully occupy an apartment, one child under four may also reside therein, except that a child under four is permitted in an apartment lawfully occupied by one person. No residual floor area of less than 80 square feet shall be counted in determining the maximum permitted occupancy for such apartment. The floor area of a kitchen or kitchenette shall be included in measuring the total liveable floor area of an apartment but the floor area for private halls foyers, bathrooms or water closets shall be excluded.
(2) A living room in a rooming unit may be occupied by not more than two persons if it has a minimum floor area not less than one hundred ten square feet in a rooming house, or 130 square feet in a single room occupancy. "