It takes time and energy to clean the veggies, peel the fruits and make the juice. I hope that with the chaotic schedule of a teenager you can manage it.
I find that I do best with green veggies accented by fruits. The nice thing is that one can put organic lemons into the juicer unpeeled. The peel contributes bioflavanoids, which are really good for you.
Oranges and grapefruites need to be peeled. Their peel contains something that isn't good in quantity. Don't remember the details.
So, scrub the carrots and put them through the juicer with a whole or cut up lemon. Much easier!
Give your dad a diluted glass now and again. Even if he doesn't fast, the juice is nourishing. I know many people who drink juice for two meals and eat one. That is better than nothing!