The structure of the metal guanadinium formates is analogous to perovskite; the Cu compound is of particular interest as a potential multiferroic. We have recently demonstrated that solid solutions between different transition metals readily form in this family. Substituting Mn or Co for Cu disrupts both magnetic and - because only the d9 Cu ion exhibits significant Jahn-Teller distortion - electric ordering. Although X-rays cannot easily discriminate between these metals, preliminary scans on SXD show that in mixed-metal compounds the unit cell doubles in two directions, indicating cation ordering. On this basis we here propose a full single-crystal structure determination. In this work we aim to elucidate long-range cation ordering in three mixed-metal frameworks in this family. This will complement a simultaneous total scattering proposal focused on short-range order.