The head is composed of a head sample, first head bone at the end of the neck and two duplicates of that bone in the head and jaw themselves. It never generates anything past the neck and pieces cannot be individually controlled.
I would very much appreciate any help, and sadly cannot attach any images, probably because this is a free account.
Edit: I have managed to extend it to control the head, but the jaw is still uncontrollable
It can't, I'm putting one together as a custom for it to work as rigify can also work from customs.