We investigated computationally the alpha-, gamma-, and beta-isomeric structures, relative stabilities, and the electronic and basicity properties of magnetic [(V14E8O50)-E-IV](12-) (hereafter referred to as {V14E8}) heteropolyoxovanadates (heteroPOVs) and their heavier chalcogenide-substituted [(V4EE8O42X8)-E-IV](12)- ({V14E8X8}) derivatives for E =Si-IV, Ge-IV, and Sn-IV and X = S, Se, and Te, We used density functional theory (DFT) with scalar relativistic corrections in combination with the conductor-like screening model of solvation. The main purpose of this investigation is to introduce the structure-property relations in heteroPOVs as well as to assist the synthesis and molecular deposition of these molecular vanadium-oxide spin clusters on surfaces. "Fully-reduced" polyoxoanions {V14E8} and {V14E8X8} are virtually comprised of [(V14O38)-O-IV](20-) {V-14} skeletons of different symmetries, that is, D-2d for alpha-, D-2 for gamma-, and D-4h for beta-isomers, which are stabilized by the four {E2O3}(2+) and four {F20X2}2 moieties, respectively. Our DFT calculations reveal stability trends alpha > gamma > beta for polyoxoanions {V14E8} and {V14E8X8}, based on relative energies and HOMO-LUMO energy gaps. The a-isomeric polyoxoanions {V14E8} and {V14E8X8} with the high negative net charges may easily pick up protons at the terminal E-O-t and E-X-t sites, respectively, which is evidenced by strongly negative enthalpies of monoprotonation. Energetically favorable sites on polyoxoanions alpha-{V14E8} and alpha-{VAX(8)} for electrostatic pairing with countercations were also determined. Among beta and gamma isomers, the hitherto unknown gamma[V14Sn8O50](12-) and gamma-[V14Sn8O42S8](12-) seem to be the most viable targets for isolation. Furthermore, these Sn-substituted polyoxoanions are of high interest for electrochemical studies because of their capability to act as two-electron redox catalysts.