Sky pencil turning brown
Japanese hollies grow best in light, moist, well drained soil, slightly acid soils. They are sun or shade adaptable. The plants are fairly young and are struggling to get established.
Check the drainage in the area. Japanese hollies can be susceptible to a root rot due to poor drainage and heavy soils. Check the soil several inches deep and water whenever dry up until the ground freezes. Keep mulch no thicker than two inches in depth and away from the base of the stems.
Scratch the branches and look for green tissue. If you see it, the stem is still viable. Prune all dead stems back to healthy tissue.