This study presents the synthesis and characterization of Cs2NaBiCl6 nanocrystals (NCs) doped with varying concentrations of In3+ to improve their luminescent properties. Utilizing a colloidal solution method, we systematically varied the In3+ concentration to identify the optimal alloying level for enhancing the photoluminescence (PL) properties of the Cs2NaBiCl6 NCs. Structural analysis confirmed that the In-alloyed NCs maintained high crystallinity and a uniform cubic shape. The optical properties were significantly improved with the In3+ alloying, reaching a peak photoluminescence quantum yield (PLQY) at an In/(Bi + In) ratio of 0.7. This optimal alloying concentration led to a nearly 2-fold increase in the average exciton lifetime to 6.98 ns, indicating an enhanced self-trapped exciton generation and improved radiative recombination efficiency. Temperature-dependent PL spectra revealed that the Cs2NaBi0.30In0.70Cl6 NCs exhibited a higher exciton binding energy and longitudinal optical phonon energy compared to the undoped NCs, suggesting superior thermal stability and reduced nonradiative recombination pathways. Density functional theory (DFT) calculations were employed to elucidate the charge density distribution, highlighting significant charge localization at the In-Cl and Bi-Cl bonds, which is attributed to the enhanced charge mobility in the alloyed NCs. The findings of this research not only address the limitations of current lead-free perovskites but also establish In-alloyed Cs2NaBiCl6 NCs as a promising candidate for blue light-emitting devices. This work advances the development of environmentally friendly optoelectronic technologies.