Aw,my heart is aching. This thread is very difficult for me to read, I can't imagine what it must be like for you to have to live this.
I hope you can find a friend for your other gander :(
20 years is a long time to share your life with someone, even if it was "just a bird" to other people...
I've also read that green poop can indicate starvation. Can you feed him some hard boiled eggs to help give him a boost and also poultry nutri-drench as additional supportive care while you administer the penG. Just ensure you give the full course of antibiotics and don't stop early.
Praying for...
I've never given a goose a shot, but if you have no other choice, do what you feel is best. How were you able to get PenG without a vet prescribing it for you? (I'm just confused about how it came to this)
Hope your gander shows improvement.
Warm it in the syringe between your palms rubbing back and forth. Make sure you keep the needle cover on while you do it. You don't want it hot, the heat lamp is unnecessary.
Hope your chicken does okay.