The effect of added nonadsorbing macromolecules on the phase behavior of suspensions of electrostatically stabilized cellulose nanocrystals is examined. Triphasic isotropic-isotropic-nematic equilibria develop in cellulose nanocrystal suspensions to which a mixture of dextran and blue dextran is added. Phase diagrams for different combinations of uncharged dextran and anionically charged blue dextran are presented. The range of dextran concentrations at which the triphase equilibrium is produced is strongly influenced by the molecular weight of the blue dextran. Reentrant phenomena as well as regions of biphase coexistence are present in the phase diagrams. A threshold difference in charge density between two blue dextrans of varying degree of dye substitution is necessary for triphase equilibrium to occur at a given number density of each polymer species. Different repulsive electrostatic and attractive entropic forces may dominate at different concentrations of the dextrans, contributing to the rich phase behavior of these suspensions.