I am so sorry.
Seems like you didn't start off with healthy chicks or adults to begin with.
I highly recommend ordering from a well known hatchery next time.
You are far more likely to get healthy disease free chicks.
It's very sad that people sell sick birds, although some may not realize they are selling sick birds to begin with.  There are a lot of people that knowingly sell sick birds.
I am sorry for your loss but look forward to hearing what the necropsy report says.
Hopefully you can pass the report info on to the seller and maybe they will refund you all of the monies you have been spending.