If your written lease with your landlord states no pets in your unit, then your agreed to no pets. The terms of one's written lease controls the obligations owed by the tenant to the landlord and vice versa over the rented unit in the absence of conflicting state law.Whether or not your landlord has known about the cats in your unit or not is not really the issue now that he has advised you in writing that they must go as they are not allowed under the terms of your written lease within a set time period.Felines have not been qualified as disability pets, only canines.You need to comply with your landlord's request to get rid of your cats in the stated time period or be faced with a situation of being in breach of your lease where the landlord may terminate it.