Well let me start with your first question and it could be a good part of your entire problem. You are filling the babies crops way way too full. If they are throwing up food that’s a good indicator you’ve gone too far and the opening and closing amid the beak and turning blue is classic signs of aspiration pneumonia. The babies at this size are going to get just a few drops really. Still pretty thin and just full to the point where it would start to turn towards going up the throat without going up. It needs to stay as a little beach ball on their front. If it’s up the throat at all it’s too full. If in 2 hours it’s not empty there are three possible problems 1) the babies are too cold. 2) the food is being fed too cold. 3) the food is being fed too thick. I don’t know how old these guys are and the closest babies I have to compare is tiels I’ve not had to say one care for any of my keets so far
I’m willing to help where I can ideally if possible foster them with another bird for at least 2 weeks
