We were probably doing the same thing, i just turn the sensitivity of the brushes way down:
Once you get the faces scaled & lined up as best you can, select the uppermost layer that you want to blend down, grab the eraser tool, make it as big as you can (size 100 if you have room on your canvas), set the edge to 100% to make it soft, and turn the eraser opacity way down, and working from the outside inward… slowly brush the unwanted stuff away. The rest is just tinkering with opacity of the individual layers, adjusting hue, saturation, brightness, contrast, etc, (stuff I know you do all the time).
It’s actually better to use masks than to erase on a layer, because masks won’t deface the image (they just hide portions instead). But for quick & dirty fun… the eraser can be your friend.