The co-doping of double perovskites is a useful approach in terms of improving their stability and photoluminescence quantum yield. Herein, Bi3+ and Te4+ cations have been co-doped into Cs2AgInCl6 nanocrystals. Doping with Te4+ cations promotes radiative recombination of self-trapped excitons due to increased defect formation energies of silver and indium vacancies, according to experimental and theoretical results. When used in excess, the TeO2 precursor would generate residual TeO2, Te2O3Cl2, R2TeO, or all three of them, which confined undesired chlorine ions on oxygen vacancies to counteract the pull from the Cs2AgInCl6 host, resulting in improved coordination with surface oleic acid ligands. As a result, 1% Bi and 8% Te co-doped Cs2AgInCl6 nanocrystals reach a high photoluminescence quantum yield of 34% and show an improved stability, maintaining over 70% of their original emission intensity after storage for more than 1 month. These findings are important in the context of producing high-performance properly doped double perovskite nanocrystals for optoelectronic applications.