Has your dad tried Emend. That did wonders for my nassea. Also, please make sure that he is drinking water, or any liquids he can get down. It will make him feel better and prevent dehydration which can just overwhelm you even after chemo, very easily.
This is so hard, but you're right, keep his eye on the "prize".
Wishing you both the best, and you've certainly got my prayers coming.
Joan