Spontaneous CuPt ordering induces a band-gap reduction $\ensuremath{\Delta}{E}_{g}$ relative to the random alloy, a crystal field splitting ${\ensuremath{\Delta}}_{\mathrm{CF}}$ at valence-band maximum, as well as an increase of spin-orbit splitting ${\ensuremath{\Delta}}_{\mathrm{SO}}.$ We calculate these quantities for ${\mathrm{Al}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{P},$ ${\mathrm{Al}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{As},$ ${\mathrm{Ga}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{P},$ and ${\mathrm{Ga}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{As}$ using the local density approximation (LDA), as well as the more reliable LDA-corrected formalism. We further provide these values and the valence-band splittings $\ensuremath{\Delta}{E}_{12}$ (between ${\overline{\ensuremath{\Gamma}}}_{4,5v}$ and ${\overline{\ensuremath{\Gamma}}}_{6v}^{(1)}$) and $\ensuremath{\Delta}{E}_{13}$ (between ${\overline{\ensuremath{\Gamma}}}_{4,5v}$ and ${\overline{\ensuremath{\Gamma}}}_{6v}^{(2)}$) for these materials as a function of the degree \ensuremath{\eta} of long range order. In the absence of an independent measurement of \ensuremath{\eta}, experiment is currently able to deduce only the ratio $\ensuremath{\Delta}{E}_{g}/{\ensuremath{\Delta}}_{\mathrm{CF}}.$ Our LDA-corrected results for this quantity compare favorably with recent experiments for ${\mathrm{Ga}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{P}$ and ${\mathrm{Ga}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{As},$ but not for ${\mathrm{Al}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{P},$ where our calculation does not support the experimental assignment. The ``optical LRO parameter \ensuremath{\eta}'' can be obtained by fitting our calculated $\ensuremath{\Delta}{E}_{g}(\ensuremath{\eta})$ to the measured $\ensuremath{\Delta}{E}_{g}(\ensuremath{\eta}),$ and by expressing the measured $\ensuremath{\Delta}{E}_{12}(\ensuremath{\eta})$ and $\ensuremath{\Delta}{E}_{13}(\ensuremath{\eta})$ in terms of our calculated ${\ensuremath{\Delta}}_{\mathrm{CF}}(\ensuremath{\eta})$ and ${\ensuremath{\Delta}}_{\mathrm{SO}}(\ensuremath{\eta}).$ We also provide the calculated x-ray structure factors for ordered alloys that can be used experimentally to deduce \ensuremath{\eta} independently.