Did they possibly hatch out a few days before you noticed them? If they were sitting there in the incubator for a few days before you saw them it might have messed them up...
Born with rectal prolapse??? Not to sound gross, but i'm interested in seeing pics of that. Not to insult you, but you're positive you weren't looking at retained egg yolk and such? Didn't think so...
If you're comfortable showing pics of the inclosure you're keeping them in it would eliminate my concerns that they are not being housed properly. The only reason i say this is because 80% is a very high number. I'd expect what you've described to afflict 10% or less of any given clutch. In my experience (including veileds) most babies that are strong enough to leave the egg will survive and do well if cared for properly.
I feel for you and I hope the situation improves.