Aww good luck with your little ones eye! It's no fun when they don't appreciate a treatment but at least you know you are doing what is best.
The little caramel colored chick could still be a buff. It's actually really common to have a bit of black or blue etc on the wing feathers and or tail as buff is actually often partridge based in silkies. The non buff color coming through is often referred to as "smut". It'll be interesting to see how she/he develops though!
Hmmm is your little cockerel significantly lighter than the others as well? I've got some less fluffy silkies that look small but when you pick them up aren't actually any smaller than the others.
I have had a couple very small girls that ended up developing bad wry tail (scoliosis). I hadn't thought to breed them since they had the wry tail issue but it would be nice to know if the extra small ones shouldn't be bred even if otherwise healthy.
I don't think I've ever seen one but I could have missed it. It sounds like it would be a fun thread though!