Step1. Setup the Head Deformation Node.
The first thing we're gong to do is make sure that the deformations to the mouth and jaw are connected to a blend shape and not directly to the character's mesh. Why? For starters I like to have my character to have as few controls in the camera view as possible. I don't want to be trying to pick the arm Ik handle and accidentally pick the head controller. Secondly, I don't want to have to worry about parenting issues and world space coordinates and double deformations with a whole bunch of controls that need to follow along with the rest of the body. If you just make one main blendshape for deformations, you can do whatever you want to it way off in the nether regions of your scene and not have to worry how it connects to everything else You can also separate out all of your skinning setups if you want: one for the mouth, one for the eyebrows, another for squash and stretch, etc. Lastly, since you'll be connecting up all the different controls under one control object/slider/custom UI, it doesn't really matter where you facial deformations come from, does it? You might as well keep it all nice and organized as opposed to trying to cram all of these deforms on one mesh.