Yes, it is going to give him a little discomfort the first couple of times, until he builds up a little tollerance... then he gets 100% of the benifits with only a small percentage of the headyness. Tell him not to fight it, it is ok to feel buzzed, he wouldn't complain from a buzz you get from an after meal sherry. I think you should make it a more positive experience for him. Play nice soft music etc...
Unfurtunatley there is no medical proof as far as I know that says that it will help for nausea, but it should give him an apetite and improve his general wellbeing. If he is allowed sugar, buy some candies and chocolates to munch out on... I find the sugar rush tends to counter getting too high a little.
Your dad will need to smoke at least a joint every now and then... the whole one... If there is a nice park or piece of nature that is private, maybe a friend's farm... it would be nice to have a picnic with him and let him enjoy the riches of nature and seeing it through the fresh new eyes of the herb.
Most of us started just takeing a puff here and there from friends and got plenty goofed... let him progress at his own speed.