It sounds like you are getting through this, although loosing all those chicks is terrible! I guess it's a breeder to avoid in the future?!
You will likely have issues in the future, and in these circumstances, I'd be feeding medicated chick starter to all my new chicks for at least another...
What a mess! I can see needing to treat them, and having multiple chicks from different sources is hard. Medicated chick starter isn't meant to treat sick birds, as you know, and you certainly had sick babies from that breeder! What has she said about it all?
Mary
How were your first chicks, the group who died, managed? Were they on medicated chick starter until two weeks after they were exposed to your soil! Was it extremely wet during that time? If you either didn't have them on the medicated feed, or stopped it when they went outside, that could...