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Early Fall is the best planting time for your growing zone. You are now in early winter and this is very late to attempt to plant the trees.
They will have very little time or any time to become established in the ground. The roots could freeze quite easily and you will have dead trees come spring.
If the garden center you are purchasing from will guarantee the trees and replace if they die, then you have nothing to lose except time and effort.

A soil test can be done easily. Contact your local County Extension office and they will be able to help you.
Here is a link to help you locate your closest office.

https://www.gardeningknowhow.com/extension-search/

These articles will have more information for you.

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/raise-acid-level-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/lower-acid-soil.htm

https://www.gardeningknowhow.com/ornamental/trees/hemlock/growing-hemlock-trees.htm

Planting stress may have caused initial needle drop.
Watering is key; daily for the first 2 weeks.

Continue watering and they likely will green up next spring.

https://www.gardeningknowhow.com/ornamental/trees/hemlock/canadian-hemlock-care.htm
https://www.arborday.org/trees/planting/bare-root.cfm

Yellowing can be a sign that the plants' roots are not in well drained soil. Can also be a sign of higher than normal ph levels (conifers are acid-loving plants - low ph).
Canadian Hemlock are also very sensitive to drought, so if you have had dry weather you will need to water your tree.
They are also susceptible to the Wooly Adelgid pest.
These links have more information.

https://www.gardeningknowhow.com/ornamental/trees/hemlock/canadian-hemlock-care.htm

A diagnosis such as this requires a fair amount of investigation. Were the needles discolored before they dropped? How old is the tree? Was anything sprayed near the tree? Here is an article that will help you get started with a diagnosis: https://www.gardeningknowhow.com/ornamental/trees/tgen/why-conifers-drop-needles.htm

Do a Goggle search for Weeping Hemlock, you should be able to locate a grower that can ship to you.
We do not promote any specific sellers.

Don't remove more than 25% of the branch, or of the entire foliage in a one year period, is the rule of thumb for best management practices in pruning.
Be conservative and don't remove all the foliage on a branch, leaving a bare stub. It's ugly and on a conifer it may not re-foliate.