Holly looks bad
 

I had a dozen Ilex meserveae 'China Boy' and 'China Girl' planted about 6
years ago. They are planted along the east and north sides of my house as
part of the foundation plantings. Two of them look wonderful and have grown
large. Two died. The rest are very unsightly and shaggy,. They have
mostly bare stems with clusters of leaves at the ends. What's strange is
that they are all growing in the same area with the same soil, fertilizer,
and water. They all get about the same amount of sun each day. Also
growing in the area are azaleas (some look great, some died, and some are
so-so), fothergilla, vibernum, Magnolia virginiana, stoke's aster,
pulmonaria, hosta, heuchera, lily of the valley, pumula spruce, Japanese
Maple, spriea (lemon princess, little princess, and Anthony Waters), and
lots of daylilies.

Can I cut the holly back to encourage it to branch out and form a more
dense, leafy shrub or should I just remove them? Any ideas why this
happened?

Cutting back would best be done in the early spring to make the buds
further in wake up.