I'm so sorry to hear this, Cleo. It's not all that uncommon for some hybrids to prolapse when laying their first eggs, because often the early ones are much larger than they will be once the bird settles down, and may contain double yolks. This is because two egg cells have been released at once, instead of only one, resulting in a huge egg. However, with careful management this shouldn't be a terminal problem in a young pullet. Did she come back into lay after prolapsing, and how did you treat her when she had the prolapse?
Sour or impacted crop an usually be treated by gently trickling olive oil down the hens throat, taking care not to choke her, and then massaging the crop to soften the blockage. Impacted crop can be caused by a hen eating long grass or similar vegetation, as she then can't pass the resulting hard mass. Or sour crop can be a digestive upset where stale food ferments in the crop and if it's this, there will be a really bad smell from her mouth and her crop will feel soft and squishy. Others on here have had nor experience than me with dealing with these problems, and will probably advise you. Probiotic yogurt may help if it's sour crop, and a vet may possibly prescribe antibiotics if he thinks it might be a bacterial infection. Who advised you to cull her, I wonder, was it your vet? I do agree that often this is the kindest thing to do, but it depends on the nature and severity of the crop problem, and also whether you feel her prolapse problem was completely resolved.
Have you contacted the breeder you got them from, about the problems? I'm sure it's not your fault, and possibly it might be a problem that at least one of them came with, which has been developing in the past few weeks.
And what about the worming issue? Are you certain that she has been treated with a recent full course of Flubenvet, as otherwise worms may also be involved, for both of them.