That looks too bald to be rooing, I think. And wool slip from stress doesn’t usually leave totally bare skin either, although it can; it usually comes away after there’s been a bit of regrowth so that there’s at least some fuzz of a covering.
On my screen it looks to almost certainly be some sort of parasite. Get a scraping from the edge of the area to the vet if you can. If it’s lice or similar, they will quickly scurry away from the light, so you need to do it at the edge of the area, and quickly, as soon as you lift the wool away from the skin.
However, catching the little blighters can be difficult, even for a vet, so you may find there’s nothing to find in the scraping even so. In which case the vet should be able to advise the best product to use for the most likely candidates.
Here, we use a Spot On if necessary for winter lodgers. You can part the wool along the spine, between the shoulder blades, to expose the skin well enough to get it onto them.
In the past I have also used Crovect to treat sheep for extoparasites in winter. Again, part the wool along the spine, in this case the product is applied in a line as close to the skin as possible, using the fine point nozzle.
I think the meds themselves are not contraindicated in pregnancy, so presume it is the handling which you’d rather avoid. However you would have had them shorn had the weather been better
In the UK we don’t shear pregnant ewes, but I know they do in some countries. But the stress of a pour-on, or even an injection, is surely less than for shearing.
Having been a newbie sheepkeeper myself in recent enough memory - thirteen years ago for me - I can tell you that yes, handling by people they don’t know, and especially by inexperienced people, can be quite stressful for them, and can cause problems in pregnant ewes. Once they know you, and you know what you are doing and handle them competently and confidently, stress is significantly less - for them and for you!
. But it looks as though you may have a medical issue that will cause worse problems if you leave them.
Do you have a farming neighbour who could help you? Or even would the vet help you treat them, or at least get you started with them?
If it is parasites, you will need to treat them all on the same day, and probably then move them to a different field / housing or they will get re-infected. But again, the vet will advise once the culprit is known, or on the probabilities.