Screen projected shader with lighting used to blend between textures

I am aware that this is a quite specific questions, but maybe there are some ShaderLab-Experts around who can help me.

I am currently trying to develop a specific look for a game, or rather the technical details for a look I created some 4-5 years ago for a short film I never finished, and I need a rather specific shader for that. I would need the shader to dismiss all UV informations of the models and use the screen coordinates instead. Also I would like to use the shading to blend between at least three different textures (more would be even nicer), one for illuminated areas, one for half shaded, one for full shadows. The final output would be unlit, so it would show the raw color information of the textures.

I am not asking for a complete shader, I am just asking if anyone knows if it is possible to achieve all of the above and where I could start.