We report Monte Carlo results for the thermodynamic and structural properties of a mixture of equally sized hard discs that are characterized by a nonadditive collision diameter for particles belonging to unlike species. We calculated the phase-coexistence lines relative to fluid-fluid demixing using a first-order perturbation theory. We also analyzed the onset of structural ordering in the mixture within a one-phase scheme based on the multiparticle correlation expansion of the statistical entropy, an approach that has been already used to study demixing in three dimensions.