The final state distribution of the first six electronic states of $^{3}\mathrm{HeT}{}^{+},^{3}\mathrm{HeD}{}^{+}$ and $^{3}\mathrm{HeH}{}^{+}$ resulting from the \ensuremath{\beta} decay of ${T}_{2}$, DT, and HT are calculated, to satisfy the higher-resolution requirements and increased sensitivity of the future tritium neutrino mass experiments. The sensitivity of the initial temperature, ortho-para ratio, and isotopic composition of the source is considered. Estimates of the error in the value of the neutrino mass deduced from fitting, due to uncertainties in the temperature, the ortho-para ratio of ${T}_{2}$, and the percentage of DT molecules in the source are presented.