I decided to try using the Rigify (Pitchipoy) Add-on and watched a tutorial on how to set it up. When they where working on the face they parented the jaw without weight paints, just normal parent and it looked like the jaw was 2 separate objects from the rest of the mesh, the upper and lower jaws each their own. I was wondering how I should model the jaws for this. Should I make separate meshes for the upper and lower jaws and parent them to the mesh and to the armature? If so, how do I make it so when the character opens his mouth and jaw it doesn't saperate and you see the inside of the back of the head? Basically, how do you model the inside of the mouth for this rigify (pitchipoy) add-on?
When rigging you need to be clear about what you want to achieve, because every little function takes time to accommodate for. Which also means that I cannot give you the perfect answer unless you describe your character more clearly. If you want a character with a normal organic jaw, then skip the following paragraph.
The only reason you would parent something without weight paints is if you want a ridged object attached. If this character had an iron jaw for example, it might make sense. I'm not sure if pitchipoy is built for that, but if you were to attach it to just one bone you could probably achieve a ridged effect. However, that would make some mesh items harder to track down. So i'd recommend a ridged bind (flood the influence to one bone) that is IF you want a ridged jaw.
If you want a normal organic jaw, then ignore your tutorial and find a better one because organic meshes generally require weight binding. I'd follow the official video for that: https://www.youtube.com/watch?v=-dwCXMc2V0U
The only thing i'd advise making into separate geometry is the teeth and tongue. That's just so that it's easier and more clean of a job when weight painting. Teeth can have ridged weighting, tongue can have auto weights. For the mouth, it's just a concave section of geometry, and of course attached to the rest of the surround mesh. You will need to ensure that the weights do not collapse the geo into the teeth and tongue when the character open's it's mouth.