I remember one time my chicken had a bad respiratory infection... I took her to the vet and he gave me tablets to dissolve in X amount of water. She got bad fast, looked to be near death and gasping for breath, with a swollen face. I decided she most likely would die, why not crush an entire tablet and force it into her? Why not try one more desperate thing to save her? She was going anyway....
The overdose saved her in this case. I don't know why it worked, but it did.
To be clear, not saying to give them more, but my chicken made it on a big OD. I hope your birds are OK. Are the others still standing?