I think the loss here is in not knowing if the ewe could be dilated when she was first in labor. Had the vet come when called and tried, we would know a lot more than we do now. But I suppose, that said, it is going to have to be the jumble presentation as cause and that she eventually dilated when one got a little ahead of the others. I don't know why the lambs died except possible tangled, broken and squashed cords in utero.
As for mine, that showed water bags, it was metabolic mayhem that lambing and ewes suffered from many different symptoms and troubles that year and with no labor at all, I think it was the calcium problem in these two which is very fixable in a year's time.
I wouldn't cull her. The odds of that happening again cannot be very great.
As to the others, it rare on our place that a ewe dies on her own. If the vet and I have exhausted our ability to help without improvement, we shoot. Everyone should be prepared to shoot and deliver their own lambs within 4-5 weeks of lambing. My vet told me that I can even wait until the legs have stopped kicking to do it. He doesn't but I can. He said he had a customer video tape himself delivering a calf from a dead cow and the guy literally sawed for a half hour and finally delivered a live calf. You don't have a half hour in sheep but you have time. And then you milk the dead ewe if possible. I guess I saw the whole procedure on my best, favorite ewe 6 weeks to lambing and he pulled out a bag of triplets and when they were spread on the ground, I said, "Geez, they are even cute with no wool." I will say that in nervousness, we would shoot about 3 times in the head just to be sure they aren't feeling anything.
I have been through a lot, I know the time to shoot (which can be the tough part with favorite ewes) but that is the first thing I would do anywhere close to lambing, cut them open.