The Earth's core contains, in addition to iron, 5-10% nickel and many light elements such as C, O, Si and S, among others. For this work, we consider binary Fe-Ni alloys with 10% Ni as host material, doped with light elements as impurity atoms. The phases considered for the Fe-Ni host alloy are face-centered cubic (fcc) and body-centred cubic (bcc). At different concentrations of 2.5-50%, the impurity atoms C, O, Si and S were placed in the host Fe-Ni alloy to create ternary alloys. The resulting ternary systems are exposed to a pressure equivalent to that existing at the Earth's core. As shown by their formation energies, these alloys are stable and advantageous. The calculation of the resistivity of the impurities was performed with the help of the Kubo-Greenwood formula. Compared to fcc, in the case of bcc, electrical resistivities begin to saturate at about 30% of the atomic concentration of the impurities. Thermal conductivity was also determined from electrical resistivities calculated for varying concentrations and pressures according to Wiedemann-Franz law. In the case of compression, we observe a rise in thermal conductivity of about 1.5% of the core's internal pressure. The reported thermal conductivities support the notion of maintaining a convection-induced geodyanmo.