Write to multiple render targets in UE4

I want to write a .usf shader that outputs to color, depth and normals but I can’t figure out the documentation.

It seems I have to use a SetRenderTarget() which takes a RHICommandListImmediate and a RenderTarget texture. But I want the render target to be 3 gbuffers (not a texture2d picture) and generate a DrawPrimitiveUP() fullscreen screenspace quad in the world. How do I do this?

I also saw something called GSceneRenderTargets somewhere. Where can I find documentation and usage examples for this stuff?

Side note: Where can I define at which render stage do I insert my shader? For example I want to inject it before the deferred lighting stage.