I'm so sorry that you're having to deal with this issue. I just came to the forum because, after three weeks of nursing our seven AE infected chicks, we just put three of them down. My husband did it with a hatchet and said it was quick. I, however, have been crying my eyes out. I got so attached to them while hand nursing them for so long, I'm heartbroken. I got to know their little individual personalities so well.....
So, I'm writing this because, as I was saying goodbye to the chicks, I realized how much easier it would have been if we'd done it right away, while they were miserable and sick. I clung to the hope that they would recover but they haven't. In all honesty, the four that we are still nursing will probably have to meet the same fate. They just aren't growing and they still can't walk properly. I just wasn't ready to give up on all seven of them at once. I picked the three whose legs were completely useless to say goodbye to today.
It is also worth mentioning that one of our AE chicks did recover enough to go back with the healthy chicks. However, he never showed as bad of symptoms from the start and we were able to put him with the healthy babies within a week. He was always able to stand up and walk, just a little wobbly. And, he will probably always be a little wobbly and smaller than the rest. He's definitely at the bottom of the pecking order and they all pick at him. So, if you have chicks who don't show good recovery within the first week of showing symptoms, I would (hesitatingly) tell you to consider euthanizing early on, before you get too attached to them. I know it's awful to say that, but my sick chicks have no real life. They can't even get to the water by themselves, I have to help them several times a day. It's not fair to them and it's probably selfish of me to keep them alive. But they are very bright-eyed now that the disease has run its course so it's hard to give up on them....
Good luck with your situation. I know it is a difficult thing to deal with. At least for me it is. These chickens are the first pets I've ever had that were my own and it's been just an awful experience.