Hi, 

Do you know when you planted them, whether it was a rootball wrapped in burlap or a container plant? If it was a container, were the roots loosened before planting? If wrapped in burlap, was that removed before planting? It could just be going through transplant stress while it focuses energy into adapting to the location and condition and establishing roots. Some plants suffer some dieback while this happens. 

Have you monitored for watering needs? Trees take about 3 years to become established and need to be watered regularly while they do. Mature trees need about 1 inch of water a week to not suffer root loss from drought. Since they are located under and near large mature trees, any rainwater that falls is going to be sucked up by those roots first, so it's crucial to feel the soil around the plant for water. The link provided will detail how to check soil moisture and how to water to fully soak the root zone. 

Have you noticed any deer browsing? We can't tell from the photos you shared if it looks like deer have eaten any of the leaves. American holly is not usually their favorite, but they do eat it from time to time. You may want to put some fencing around it to exclude any wildlife. 

If you want to prune off the bare branches, that may help the plant put energy into becoming established and focus on growing more roots. You will want to make sure the bare branches are dead, though, so if they are still pliable, you can gently scratch the bark with a fingernail or the edge of hand pruners or a pocket knife, and if it's green underneath, then give it time to see if it recovers before removing it. 

Some additional resources that may be helpful: 

What causes trees and shrubs to die

Planting a tree or shrub

Let us know if you have further questions. 

Emily