This study investigates high-entropy CrMnFeCoNi alloys with reduced Co content using density functional theory. The muffin-tin orbital method and coherent potential approximation successfully predict experimental values for volume, magnetic moment, and elastic constants. Thermodynamic properties, analyzed using the Debye–Gruneisen model, emphasize the need to consider both electronic and magnetic contributions to the free energy. The alloys exhibit anti-Invar behavior, with a significant increase in the linear thermal expansion coefficient with increased temperature. This effect is slightly more pronounced for reduced Co content, leading to a larger lattice parameter and a decrease in elastic constants. However, the changes are small, suggesting that similar mechanical properties can be achieved with lower Co content.