I'd say yes. As @dawg53 said, if one has them, most likely the rest do as well. You may be able to add that dewormer to their water? But I'm not sure. Hopefully some other posters can confirm this.
Strange. Are those two different-lookimg ones the same age? It's been a couple of years since I raised GLWs so I don't remember the feather stages clearly.
I think those may just be baby feathers thar will soon fall out and be replaced with adult ones. You can see some that are already in and they are gold.
Aw! I love that stage. And it's true, chicks love interacting with you and stuff but when they get older they get skittish and they don't want to be touched. I wonder why.