If memory serves me correctly these are recently born lambs so they are in the dead zone, that is most lamb mortality comes within the first 21 days of life. For the first three days a lamb does okay because they are still on the reserves of their mother, so from the 3rd day to 21st day, I am on guard.
In my experience, when lambs starting looking lethargic, because of their nature, they are VERY lethargic. Starvation is the leading cause of lamb mortality, not just on my farm, but overall, and so now I just pull the lambs and have bottle lambs. As much as I dislike bottle lambs, I dislike dead lambs even more. Grafting lambs to a new ewe is really difficult with sheep, so I don't even bother to try. Formula is expensive granted, but it is better than dead lambs, and so if there is a question on whether a mother is producing enough or not, I just bottle feed.
The biggest issue is to do just exactly what the formula bag says. People often think that bottle feeding more is best because a lamb is hungry, but that is not the case at all. A lamb is hungry too when it is with its ewe, but she still lies down, moves away, or in other words keeps the lamb from drinking. Bottle feeding is the same way, giving the lambs small, steady doses of formula, but because we regulate and ensure the lamb is getting what it needs, it thrives.
Again I do not like spending money on formula, but I dislike dead lambs even more. I would just pull the lambs and bottle feed. It sounds to me like the ewe is getting some age on her and is not converting feed to nutrional well due to her teeth. At 43, I think I have the same problem!
