I'm really sorry that you lost another. But it's a month later so you must be doing something right, don't be to hard on yourself. The dark poo is cecal, it's normal. It smells way worse than most poops but normal. Wheezing isn't Coccidiosis, it's respiratory so it's good you're giving them Tylan. Do you have a good predator proof coop to move them too soon? Not sure what your climate is but they'll be really soon. Hope all is well !!