Hi Colleen, Kimberly here from landscape solutions for you. Thank you for asking the question on taking clippings from your father's Holly shrubs.
The key to success with any type of propagating shrubs, flowers, or herbs is to have the right ingredients. A sharp knife, rooting hormone, right soil, and watering.
Take a sharp small paring knife and make a three
to six inch angled cut above a leaf node or a side shoot. Sometimes you will find that some stems are woody. An easy solution to this is to cut closer to the tip. If you already have the clippings, purchase some root hormone. You will want to get some good soil mix, either light or medium weight. Vermiculite and humus are great material to have in the soil. You can use a starter tray, pots, or anything you have around the house. I recommend to moisten the soil and mix before you put the cutting into the soil. I use warm water. Make a hole in the center of the soil and place clipping in. Keep watered but not over watered. Allow the root sytem to get established in the tray or pot, but don't let it get root bound. You can tell if it is when you see roots coming out the bottom of the tray or pot. Times will vary on different clippings and shrubs, but periodically check.
Once the roots are established have your hole or holes ready to plant. I recommend adding some organic mushroom compost to the soil when planting. Get on a good watering schedule and your clippings should develop into healthy Holly shrubs.
I will give you a link to a page I have in my landscape article section. It has tips on propagating flowers and herbs, but this also can be done with shrubs.
The best of luck to you and let us know how you make out. Thanks again for asking your question and feel free anytime to visit and ask questions here at landscape solutions for you. Have a great day!
Kimberly