So worried

So here is the story: Some cruel and inhumane person took eight kittens away from their mother at around two weeks, taped them up in a shoebox so there were no airways, and threw them into the road. A friend of mine calls me to tell me what happened and that all the kittens had been fostered out except two. I have hand-reared kittens a few times before and had no issues. However, these two are giving me second thoughts about everything! The female is solid black and is also the runt. The male is black and brown striped. Anyway, I have had these two little stinkers for the third day tomorrow. They eat perfectly fine (Kitten replacement milk, canned not powder.) pee before and after every feeding, wobble around, purr, are super active and loud when they want something, are currently asleep and twitching on my shoulder. The issue is still no poo! Their little bellies appear to be bloated but they could be because they’ve recently eaten. I know the runt has previously used the bathroom because the day i received him there were still remnants on his tail. I have tried everything I know to try. I suppose the vet will be my next option. I was just wondering is it sometimes normal for them to go this long without #2? Am i freaking myself over nothing?