<p>In this work we present a theoretical study of the structural, electronic, and hyperfine properties at Sn and Te sites of Te-Sb-Ge and Sn-doped Te-Sb-Ge alloys with nominal compositions Ge₁₆Sb₈Te₂₈ and Ge₁₂Sb₈Sn₄Te₂₈in both the cubic and trigonal structures. Density functional theory calculations were performed using the full potential linearized augmented plane wave method and the pseudopotential and plane wave method as implemented in the Quantum-Espresso code. The effect of Ge vacancies, Sb and Sn atoms on the structural and hyperfine properties has been studied, allowing us to determine the structure of these disordered systems, the localization of the Sb and Sn atoms in the Te-Ge host material and to explain the origin of the hyperfine interactions at the Te and Sn sites. Our results are supported by X-ray Diffraction and ¹¹⁹Sn Mössbauer experiments. The hyperfine parameters at ¹²⁵Te sites are also presented.</p>