I don't know about the coughing, but I do know that sneezing was just about the most painful thing I'd ever felt.
The eating will come, it takes time. Lots of time. At just a week out he's still cooking. The healing won't start for another couple of weeks.
If he's like I was, the dry mouth will take months to over come. I'd go through 3 bottles of water with any given meal. Then one day I noticed it only took 2 and then 1. Today I can eat a peanut butter sandwich sans water :)
I had my tube remove 3 months to the day of my last radiation. At that point I could choke down some soft food and Ensure. Most things still tasted like crap, but you get used to it.
The general rule is one month of healing for each week of treatment. I know how hard it is, but healing takes time.
Hang in there,
Tom