Wendy,
I'm so sorry this nasty disease has hit your family. I'm also not entirely sure I can answer the question about how sick your father in law will get since from what I've read here it seems to vary from person to person. I can say with some certianty he will most likely be feeling pretty miserable for several weeks and he may be unable to eat enough calories orally so he should get a stomach tube inserted before his treatment begins (this is espeically important if he doesn't have much extra flesh on his bones).
He is most likely going to need someone to take him to and from treatments, perhaps not at the beginning, but as time goes on and the side effects are worse (and he will likley be taking prescription painkillers). The chemo may make him unable to keep things down for some of the time (or he may be fine).
In terms of care at home, when I went through this I didn't need someone with me round the clock, even at the end of treatment, but I did need someone checking in on me to be sure I had what I needed and was tube-feeding myself and tkaing all the other meds (painkillers, antinausea, laxatives, stuff to break up phlegm, magic mouthwash, etc.) on time when I should (because I was groggy and exhaisted and had a very hard time keeping track myself). I also needed someone checking my temp because I had some sort of infection on and off and no white blood cells thanks to the chemo. I also lost my voice entirely for three weeks (the last two weeks of treatment and a week after) and I didn't like being alone during that time because if I was really sick I couldn't have called for help--this is a contingency you may want to at least prepare for though not everyone looses their voice.
In addition, your father in law obviously has some other health issues already I didn't have,which may mean he really needs someone with him round the clock for the last weeks of treatment anyway. Again, I think it's good to be prepared for that possibility.
The good news is people do recover from this nastiness at the other end, though it can take several months and that he has a real shot of getting over this disease, even at Stage IV, espcially doing the chemo and radiation at the same time. In my opinion, he needs to fight it right now and it's a hard fight-- he deserves the support he needs to get through the treatment, it seems to me it's too early to be talking about palliative care just yet. I know this is a very personal decision, though, and I suppose at 75 I might feel differently about how much of a fight I wanted to wage (somehow I doubt it though).
I found this site incredibly helpful as I went rhough treatment. As you read more here, you'll read a lot of other peope's experiences and get a good idea of the variety of things you can expect. People are also very supportive here and you can come here and ask questions or just vent anytime you need to!
Nelie