Kim,
I'm sorry you and your dad are still going through this -- unfortunately, there are some long-term after-effects of this illness and they tend to ripple out to the rest of the family.
I agree with the others that it makes sense to talk to the doctors about the possibility that your dad is experiencing depression. If he goes to family gatherings and sees other people doing "normal" things like eating solid food, engaged in physical activities, etc., it can be a reminder of what he's missing out on right now.
I'd also suggest talking to the doctors about relief for the lack of saliva. My saliva level went way down after radiation and I've been using a combination of Salagen pills (3x daily) and Biotene products (mouthwash and gel) to get some help. Also, when I sleep totally flat on my back, the saliva that I do have pretty much shuts down, so I always try to have my head somewhat propped up during the night (I don't know if this has any bearing on your father's preference for sleeping in a recliner).
I hope your father can begin to get back to the things he enjoys doing. Many of us here can attest to the fact that we've found a lot more to appreciate and to occupy our time in "life after' cancer".
Cathy