There is only one "input", the Microphone. THere is no other signal going into the laptop. Standard Audio goes out of the laptop into the headset, and microphone audio goes into the laptop from the headset. You say you understand this, but you then ask questions that a person who understands it wouldn't ask.
You say "once you have the signal in your laptop" there is only one signal- the mic signal. Any "blending" (heck any audio portrayal of that microphone audio at all) is done through software on the laptop. Once you have a "blended" (mixed) signal, you cannot magically unblend it, In fact, it takes extra effort just to combine the microphone input stream with the system sound.
Addiitonally, you requestion that these "separated" signals magically be send down a single Phono wire. That simply is not going to happen.
And if you want it to run through the laptop and come out onto two other phono plugs... what's the point of going through the laptop? Also, there is only one audio output, so that won't work anyway.