Assuming that both pc's are in the same network i think you could "stream" your laptop webcam over lan and use it in the main pc as a remote video source, i'm not really sure about how to do it, but i believe it's possible, also you could use an smartphone(probably better camera than the laptop) with an app called IPcamera.
PD: if i recall correctly the guys of teksyndicate do something similar, they stream from different locations(in the world) 4 screen gameplay and 4 webcams, and in one server they put all together and stream to youtube and twitch. so, if that is possible, your case should be as well. I believe that you stream from the source(laptop in your case) with rmtp and in the main pc you just introduce the rmtp address, but i'm not exactly sure.