Our nutritionist recommended a Capsule Vitamins as it is easier on the stomach and it absorbs easily. Although we found Rainbow Light Womens or Men's one a day vitamins which is not a capsule but has worked excellent for my mom. It is a food based vitamin and the body is better able to absorb the nutritients (so they say). She has been taking them for almost two years now. Also, to maintain weight the nutritionist recommended a scoop a day of whey protein mixed in with yogurt (we the the whole foods brand). The whey protein helps maintain weight. Not sure if this is what you need for your dad, but it can help keep what strength he has left. Your best bet is to talk to the nutritionist at your hospital. Most cancer clinics have a nutritionst readily available to help the patients. Good luck and hope this helps.
Jaime