We have carried out x-ray structural analysis and have studied the temperature dependence of vibrational spectra and electrical resistivity under uniaxial strain for (ET)(5)Te2I6 and (BETS)(5)Te2I6 [ET=bis(ethylenedithio)tetrathiafulvalene and BETS=bis(ethylenedithio)tetraselenafulvalene]. In the low-temperature insulating phase for each salt, a charge-sensitive mode nu(2) exhibits peak splitting, and a vibronic nu(3) mode shows factor group splitting. This observation confirms the charge ordered state. The distribution of site charges is determined from the factor group analysis of the vibronic nu(3) mode, which is in agreement with that determined from x-ray structural analysis of the ET salt. In the high-temperature conducting phase, the vibronic nu(3) mode is smeared out whereas the frequencies of the two charge-sensitive modes are almost unchanged over the whole temperature range. We have proposed a model wherein the highly conducting state is ascribed to the frustration between the site-charge distributions in the insulating state and the other distribution, which contributes to a reduction in the intersite Coulomb interaction along the stacking and diagonal directions, respectively. Our conjecture is supported by the temperature dependence of the electrical resistivity under the uniaxial strain.