Unfortunately the all-brown plants cannot be salvaged, even with watering at this stage, as they are already dead. Once needles discolor like this, they do not recover, and this type of evergreen cannot regrow foliage from older wood closer to the trunk. Any individual plants that are off-color (usually a sickly olive-green hue instead of the richer green) are also a lost cause, since they cannot recover from stress or root damage that led to that degree of discoloration. It can be due to factors like over- or under-watering, but unless someone was watering on your behalf while you were away, odds are it was due to drought stress.

A significant portion of last year's growing season was impacted by drought, as was this year so far (even with recent rains), and plants not given supplemental water as needed can suffer from dieback months or even a year or more after that event. Conifers (needled evergreens) like arborvitae prefer to remain more evenly moist or have ready access to moisture (without staying wet) during periods of dry weather and high heat, as we experienced for much of the summer. While some conifers like junipers are more drought-tolerant, even they have their limits in this kind of weather. Complicating a diagnosis is the fact that drought stress can be a precursor to a secondary problem that accelerates plant damage or dieback, like wood-boring insects and (more commonly) certain fungal infections like Botryosphaeria canker. (The linked page focuses on Rhododendron, but this disease can impact a wide range of other species.)

Canker might be the cause of scattered dead branches on a still-living plant. Prune those individual brown branches off, since they will not rejuvenate. Don't worry about any with brown interior needles and a live tip, as that can keep growing (and some degree of older needle shedding in the interior is normal for these plants); just remove any that are entirely brown out to the tip of the branch.

Unfortunately, conifers don't usually develop obvious indications of drought stress until dieback manifests, since they don't really wilt. Sometimes they can discolor slightly, looking more dull once they become a bit too dry, but it can be subtle or not always apparent. Feeling the soil around six inches deep next to the root zone is the most reliable way to determine when watering would benefit them. If somewhat dry to the touch at that depth, water thoroughly; if damp when checked, watering can probably wait. We realize you weren't home to do this, but for the future, if someone is available to periodically check on the landscape plantings for you, they can use that guidance to help avoid drought impacts if the weather repeats itself. Some irrigations systems also might be programmable to run at certain intervals and include a rain sensor that will keep the system from running if enough rain falls within the program parameters. We don't have experience using these to recommend any particular system or setup, but it might be something worth looking into if this becomes a recurring issue during time away.

Although it won't be much help for this particular situation, if you would like to hire a certified arborist or licensed tree expert in the future, you can use the linked pages to find candidates. They won't be able to cure existing issues or treat every condition, but can help with preventative measures (if any are warranted for certain pests or diseases) and can help narrow-down a diagnosis by examining a tree in person.

Miri