Layered iron halides (${\mathrm{FeCl}}_{2}$, ${\mathrm{FeBr}}_{2}$) are known to exhibit several unusual features, especially in comparison with those of the first\char22{} and more commonly investigated\char22{}member of the halide series, ${\mathrm{FeF}}_{2}$. In contrast with the latter, the crystal-field excitations are dominated by spin-orbit effects and the magnon dispersion approaches that of a two-dimensional ferromagnet. For ${\mathrm{FeCl}}_{2}$, hybridization effects between magnons and acoustic phonons as well as electronic excitations and optical phonons have also been reported. After an analysis of single-ion and exchange Hamiltonians, we investigate both hybridization mechanisms on a microscopic basis. The theoretical coupling constants are found to be in very good agreement with those deduced from the experimental data in both cases.