i dont know well but this can be done using aux cable(as far as i think i can do with 100% success with two PC's). Insert the aux cable in the headphone out of Laptop 1, from realtek uncheck the box from settings stating "mute the headphone panel when speakers are working or something like that" and then connect the other jack of aux to the aux in(if there is) of your laptop 2. Else insert it in Mic jack and make it "line in" from the realtek panel.
P.S. - This guide is an experimental and expected to work. If you dont have realtek drivers, you will have to see your own what is to be applied.