Welcome to the board. So sorry to hear about your FIL. It is a tough cancer, but dont let the stats on the internet get you down. Treatments are getting better all the time.
If he is having a hard time getting in enough calories and they think they are going to do surgery, he should talk to them about putting in a g-tube. He will be able to take meds, fluid and nutrition through it. It was a life saver for my mom. She has now worked her way off from it, and is taking everything orally, but with out it she woud have died. They are leaving it in place until they decide on the surgery, as she would need it after the surgery anyway, so no sense in messing with it right now. They were able to put in her chemo port and feeding tube during the same surgery so they only had to knock her out once (the tube and port are not in the same place, but it saved them from putting her under twice).
Hang in there and please keep us posted !