In summary, we have studied a series of novel lead-free vacancy-ordered double perovskites (VODPs) based on titanium and tin, with chemical formula Cs 2 Ti 1-x Sn x X 6 (X = I, Br). We have synthesized these alloys as nanocrystals (NCs) following a colloidal route, and characterized their structural, electronic, optical and thermodynamic properties using a combined experimental and computational approach. We have also computationally characterized the mixed-cation chloride VODPs (x = Cl; Figures &) finding consistent trends in behavior. We find all phases to retain symmetry, with lattice parameters slightly increasing in going from pure 𝐹𝑚3𝑚 titanium to pure tin compositions. In agreement with our experimental observations, calculations reveal the Bsite cations to be highly-miscible in this structure, with BX 6 -2 octahedra behaving as rigid blocks and the vacant inter-octahedral space varying to accommodate the changes in cation (octahedron) sizes. We show that the mixed compositions have absorption features essentially equal to the linear combination of the pure Sn and Ti VODP phases, with this behavior ascribed to the lack of orbital mixing and weak interactions between the isolated BX 6 -2 octahedra in the effectively zero-dimensional crystal structure. From XRD measurements over time in air, we observe that Cs 2 SnX 6 NCs are stable in air while Cs 2 TiX 6 NCs show decomposition after a few minutes of air exposure. Moreover, we observed that stability increases with higher values of x in Cs 2 Ti 1-x Sn x X 6 as expected and predicted computationally, with the bromide mixtures showing higher stability compared to the iodide ones. Overall, our results further elucidate the unique properties of these compounds, where much of their behavior is reminiscent of molecular aggregates, despite a three-dimensional structural connectivity in the solid. The combination of facile cation mixing and weak octahedral interactions / orbital hybridization demonstrated in this work, with resultant intriguing optoelectronic properties such as strong excitonic binding, could lend itself to several alternative applications beyond those mentioned in the introduction. One example is potential hosts for photoluminescent defects with quantum computing applications, for which minimal interaction with the host environment is desired for long coherence times. Another is high-entropy semiconductors with lowtemperature synthesis routes, aided by the ready miscibility of the cation site -as recently demonstrated in Ref. 19.