Do NOT split the rootball. You can take cuttings if you would like. Do you know which holly you have? Do be careful how close you plant it next to your foundation. They can get very large and wide over time. Take a look at these sites.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.