That's a roundworm. The Safeguard will take care of that. I wouldn't use Ivermectin since it seems to have lost some of its effectiveness.
Dose for Safeguard is 0.23ml per pound of weight given orally once daily for 5 days in a row.
If the others a bit droopy, then treating them would be a good idea. Since they are in molt, Safeguard is known to affect feather quality in molting birds, so Valbazen is a better choice.
Valbazen dose is 0.08ml per pound of weight given orally once, then repeated in 10 days.
You can find Valbazen online. If you have a TSC, you can order online through them and pick up at the store or have it delivered, etc.
Or you can order through places like Valley Vet.
https://www.valleyvet.com/ct_detail.html?pgguid=30E07949-7B6A-11D5-A192-00B0D0204AE5