Question Wrinkle map - Need to dissolve multiple normal maps

I have 4 different normal maps for a character. I want to build an HDRP shader that can dissolve between these 4 maps depending on the blend shapes that are activated. I managed to load 2 maps and using Lerp and a slider input achieved the result I need.

However I cannot figure out how to input the other 2 maps into the same normals input for the shader. Does anybody have any ideas ? Also need to connect the shader sliders to the geo blend shapes.

Thanks

 

here is some more resource:
https://polycount.com/discussion/128959/the-correct-method-to-combine-mix-overlay-normal-maps