You talking to poor Penguin in that video was so heart-wrenching!
A few of things, and someone please correct me if I got the info wrong:
First, the expiration on most medication is not true. It's put there for government regulations, and is usually way before it loses any efficacy so as to get more sales.
Second: Antibiotics, from what I have heard and read several places, are one of the few medications that become
stronger as they get older, so you may want to go easy on it instead of more.
Third: Also from what I've read and seen, ducks can be
carriers of Bird Flu, but do not become ill to it.
If Puffin is also showing signs of something, I'm fairly sure it's some sort of virus, especially with the crusty eyes.
I'm sorry you are all going through this terrible time.

Hopefully, they can figure something out for you tomorrow! Please keep giving us updates, and know that even though we aren't physically close, we are here supporting you all with our hearts! *hugs*