Question regarding giving chicks terramycin

[Hummer]

Hello Everyone! I received my chicks 3 weeks ago and other than losing two within the first few days - everything seems to be going well. However, I have noticed a couple of things going on with 2 of my chicks.

One of my auracana bantams seems to be acting a little puny. Stands around with feathers kind of fluffed up with shoulders hutched - kind of looks like a buzzard - no really, it does!

Anyway, this chick eats and drinks but does not do so as vigorously as the others. I have noticed this chick acting this way in the past 3 to 4 days. I think it is sick.

I really don't have a good place to quarantine it from the rest and wondered if it is okay to just give them all a round of antibiotic for 7 to 14 days?

My next question is - Another one of my auracana chicks seems to have trouble seeing as well as it should. It has been like this since it arrived. It sometimes walks around and around in circles - it gets disoriented, easily, and almost appears to have tunnel vision... Sometimes when it is resting I see its head moving back and forth - almost like the chick is dizzy or its head is spinning... Also, when it drinks water, it backs up flapping its wings holding its neck and head way back and sometimes even flips onto its back. It is the strangest thing I have ever seen.

Other than that - the chick seems to be thriving. Does anyone know if this is probably just a defect or does the chick have some kind of disease that could be contagious?

Thanks for any help that can be offered!