So sorry to hear all the butterflies had problems. I really don't know what would cause it, hopefully someone here will have an idea. Last year I had three butterflies that didn't form right, they had problems with their feet, didn't form the toe hooks so they couldn't hang onto anything and fell too. So far this year I have only had two (out of 75) that had problems. One of them, a female had a little problem with its upper wings, one of them kept wanting to go under the bottom wing instead of above it, but it was able to fly so we did let it go. It was also missing toe hooks on one of its front legs, the others were ok though. The other one, a male, didn't get its probiscus (sp?) tongue, together and it dried split and hanging out. I knew it wouldn't live but we did let it go anyway. It was perfect otherwise.
Do you have any milkweeds and caterpillars that are in your area naturally? Maybe you could try some of those instead. Hope you are able to get some that are ok! We have lots of milkweed around here and that is where I get all of my eggs and caterpillars from. So far this year I have lost 5 cats and 4 crysallis but have let a total of 75 butterflies go, one of which will die (see above) but that makes 74 out of 84 that were healthy. I have lots to go yet too, more hatching daily.