While effective alternatives for PV applications rely most on tin-based compositions, several other phases containing different metals such as Bi, Sb, Cu, Ge, have been discovered and investigated. In many cases, such perovskites resulted to be not suitable for PV devices but possess very appealing optoelectronic properties which can be exploited in other applications. Among these systems, bismuth-and antimony-based perovskite derivatives of general formula Cs3M2X9 (M=Bi, Sb; X=Br, I) have shown a strong technological potential in particular in the area of photocatalysis (both for solar fuel generation and organic synthesis) and photodetection. Bismuth-based defect-ordered perovskites have been object of more intense studies with respect to the corresponding Sb systems, notwithstanding their appealing optoelectronic properties such as high carrier mobility, low trap density, and long diffusion length. As a matter of fact, Cs3Sb2Br9 millimeter-sized single crystals and nanoflakes have been applied in the fabrication of photodetectors with excellent performance in terms of responsivity and detectvity. Good photodetectors based on Cs3Sb2Br9 have been also prepared by means of chemical vapor deposition technique. Cs3Sb2Br9 and Cs3Sb2I9 revealed also to be suitable candidates for photocatalytic applications and in this respect have been, for example, applied in the photocatalytic carbon dioxide reduction, water splitting, and in aromatic C-H bond activation. Some efforts has been also applied in the possible use of these defect-ordered perovskites in the manufacturing of solar cells. Cs3Sb2I9 has been preferentially used in for PV due to its suitable band gap around 2 eV, providing good stability but relatively low efficiencies around 2-3%. While there is a clear relevant interest in Sb-based materials, many of their fundamental features still need to be explored, for example, in terms of synthetic procedures, band gap tuning by metal or halide alloying, and their electronic structure. Considering the structural and optoelectronic similarity with Bi-based analogues, which have been more deeply investigated, it appears that some tuning strategies of the photophysical properties of Sb materials should be clarified to enlarge the plethora of lead-free perovskite derivatives. For example, the preparation of mixed Sb/Bi phases of vacancy ordered perovskites has not been reported in the current literature but there is a strong motivation to investigate such a system. Indeed, a recent work on the Cs2Ag(SbxBi1-x)Br6 double perovskite solid solution has demonstrated a nonlinear trend of the band gap value as a function of x, providing mixed compositions with lower values with respect to Cs2AgBiBr6 and Cs2AgSbBr6. However, the possibility of successfully preparing a continuous solid solution within the vacancy-ordered Cs3(Sb1-xBix)2Br9 system has still to be verified. The choice of a suitable synthetic route for these Sb/Bi materials is critical due to the low solubility of halide precursors posing strong limitations for traditional synthesis procedures applied to MHPs. A viable choice could be the use of mechanochemistry which has been recently applied to Bi-based systems but never to Sb-containing perovskites or mixed compositions. Finally, the halide alloying strategy to modulate the optical properties of perovskites has still to be investigated in Sb vacancy-ordered materials.