interior browning is normal ...

they all appear to have grown.. extended this year ... so they are alive ...

what i cant tell.. if that one angled down is cracked or broken ... kinda center bottom ....

i would leave the center one alone. ...

i cant tell from the pic.. what the deal is with the left lower one ... if its grey to the tip ... then it is dead.. and should be cut back to a live part.. not necessarily all the way back ...

ken

The one in the center is going to be abnormally gaunt when the dead foliage drops or is shaken out. Usually this cultivar presents a solid outer surface which obscures or more or less completely hides the dead inner foliage. Which means there is an issue, probably insufficient soil moisture. Otherwise 'Smaragd' is more susceptible to root rot than usual for Thuja occidentalis, cannot therefore be planted where water puddles or there is another soil wetness condition.

The dead branch on the other is probably some kind of blight, unless the branch was broken. If you are in the US and available when they are open your best bet for possible plant disease issue identification may be your local USDA Cooperative Extension office. They will need to see samples of affected parts.

I will often shake some of my conifers such as emerald green arbs, conifers on standards, topiaries, and others that are shakable this time of year then remove the stuff that gets trapped inside on the bottom with my hands. Cleans em out so more light gets in and helps a tad as mulch/future nutrients. Whether or not this is good I have no idea, but I do it. I cant see any drawbacks.

Cleans em out so more light gets in

Removal of interior dead foliage won't result in new growth unless outside shell of existing live foliage is reduced.