A peg tube is inserted through a small incision in his abdomen, it is not the same as the nasel gastric tube that they attempted. I don't understand why they wouldn't try that.
If he is still in the hospital let administration know that you are upset with the quality of care and want an explanation of why he is not a candidate for the PEG tube. Dave is right about asking to talk to another doctor for a second opinion, this is a very serious situation.
If you still don't get an answer that makes sense you can make a complaint to the state health department as quality of care is regulated and patients have rights.
You didn't mention if he is getting anything for the pain, that's another basic patient right that is sometimes ignored. My husband found the duragesic or fentanyl patch was the only thing that worked for him. Are they addressing the mouth sores?
The jaw tightness is called trismus and there's good information on this website about that. Stretching exercises are crtical and a therabite jaw exerciser is often prescribed.
Are they giving him IV fluids for the dehydration?
JoAnne