We are performing structural investigations of a series of brownmillerites (Sr,Ca)2(Fe,Co)2O5 which display long-range modulated ordering of oxygen vacancies at ambient and high temperatures. We intend to refine their commensurate and incommensurate modulated structures against high resolution single-crystal neutron diffraction data, in order to complement and inform the interpretation of our INS/QENS and DFT-MD studies into the nature of order-disorder transitions and associated oxide ionic conduction mechanisms in these materials.