In this work, we report on the analysis of both vibrational and magnetic properties of heavy rare-earth molybdates Gd2(Mo0.9W0.1O4)3 and Gd1.8Er0.2(MoO4)3. The crystal structures, as determined by X-ray powder diffraction and the Rietveld refinement analysis, established that at room temperature both of these materials belong to orthorhombic Pba2 space group. Magnetization measurements showed that no saturation is present up to 8T at T=10K, and the magnetic susceptibility curves show paramagnetic behavior down to T=10K. The effective magnetic moments and possible short-range magnetic interactions between Gd3+ ions are treated and discussed. Raman spectra of both of these molybdates are similar to that of the pure compound Gd2(MoO4)3, indicating that changes in the Raman spectra due to the introduction of either Er or W doping are negligible at the subject dopant concentrations.