We simulate two populations of double white dwarf (DWD) binaries based on different star formation histories using binary population synthesis. We predict the number of Galactic DWDs detectable by TianQin and the Laser Interferometer Space Antenna (LISA), both individually and through joint observations. We further assess the accuracy of parameter estimation using the Fisher information matrix. In addition, we estimate the number of detached eclipsing DWDs detectable by Gaia and the Vera C. Rubin Observatory (VRO).