I only glanced over the first two, so my apologies if this repeats some advice.
For mouth wounds that don't require medical attention, give him an icecube to suck on or a popsicle. We have a special "cool pack" that is shaped like a cartoon character for our kids to use on "bumps".
Sometimes, though, you need to make sure that there aren't loose teeth, deep gouges, or swelling so bad that it causes more damage. My approach is this: YOU are the parent. YOU are responsible for making sure that your child receives proper and adequate First Aid. If that means someone helping you hold him down while you put an icepack on that large bruise on his forehead, applying a bandaid, cleaning a wound, inspecting, etc., then make sure that it gets done. There are plenty of stupid people (not meaning you and yours) that forego first aid end up with permanent or chronic injuries. Don't let your kid dictate who is in charge.
I have held my children's arms down while I put a wrapped ice-pack on a forehead, or cleaned out the toddler's nose. They hate them both, but both were necessary.
Good luck!