DLVO for complex solutions

I am working with a complex solution of 2 proteins and salt. I have been trying to use DLVO (Derjaguin, Landau, Vervey, and Overbeek) theory to get an approximation of the Van Der Waals attractive force ($F_{wppr}$) and the electric double layer repulsive force ($F_{el}$) between the molecules in the solution. However, textbooks only provide equations of Van der Waals and EDL forces for two types of molecules/spheres/cylinders. How can I calculate the forces for a more complex solution (2 proteins and 2 ions for example)?

$$
F_{wppr} = -frac{A}{6 D^2}left(frac{r_1 r_2}{r_1 + r_2}right)$$

$$F_{el} = kappa Z left(frac{r_1 r_2}{r_1 + r_2} right) e ^ {-kappa D}$$