It seems a little chancy. Ilex crenata (holly) 'Skypencil' is reportedly winter hardy in USDA Zones 6-8. Plants in containers are usually safe if winter hardy two zones colder than where they are going to overwinter. Here in central NJ, you're probably in zone 7, so plants winter hardy to zone 5 would be OK. If you don't have any other option, perhaps you could heel them in for winter (put rootball or entire container into a hole in the ground and mulch well), or at least cover the containers with a good layer of mulch to mitigate temperature extremes and prevent alternate freezing and thawing of the growing medium.

I'm not much help with your boxwood, but U of MD Extension fact sheet advises that yellowing of older, inner leaves may indicate lack of nitrogen. See fact sheet linked below for details on care, diseases and disorders of boxwood:

http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG52_IPM_Boxwood.pdf

Ok, thank you!!!

From my experience, i left my dwarf burford hollies, which are hardy to zone 6 in pots outdoors this past winter & they all died. If you have no choice but leave them outdoors, maybe try to wrap the pots with burlap, that might help warm them. i havent tried this & wil never will. im never again going to leave any plants in pots outdoors, its just a waste after i put too much care to them.

i also have a boxwood called winter gem. its in full sun from sun rise to set, south facing. its doing very well on the ground, it burns though in the winter but bounces back in the summer. it just loves the sun here in north jersey.