The amorphous silica (a-SiO2) and germania (a-GeO2) have a wide range of applications in glass industry. Based on a previously constructed near-perfect continuous random network model with 1296 atoms and periodic boundary conditions, we extend our study to amorphous Si1-xGexO2 models of homogeneous random substitution of Si by Ge with x ranging from 0 to 1. We have calculated the structural, electronic, mechanical, and optical properties for the series by using the first-principles density functional theory methods. The x-dependence of the variations in the properties is analyzed and critically compared with available experimental data. The mass density, volume, total bond order density, bulk mechanical properties, and refractive index are found to vary linearly as a function of x. For x = 0.5, we have also constructed six different kinds of particle immersion models to test the effect of inclusion of spherical particles of one glass of different sizes in the medium of the other glass on their physical properties. It is shown that particle sizes do affect the properties of particle immersion. Our calculations provide deep insight on the properties of mixture and nanocomposites of a-SiO2 and a-GeO2 glasses.