Several things you mention above worry me.First...you might want to NOT buy chickens from an auction and expect to get a good bird. Around these parts the only chickens that wind up at auctions are culls and chicken mill products, so you can expect to have chickens that are not in the best of health.
Second...the advice to throw medicine into these inferior and unhealthy birds will only yield birds who need medicine to keep good health. Please don't compound your mistakes by making more of the same. Two wrongs won't make a right....you'll be very lucky indeed to have a good flock from poor beginnings and crutching husbandry methods.
Third...now that you've made the initial mistake, the only recourse is to cull the obvious poor doers and feed optimally for the rest and give it time to see who thrives, who does not. Those that do not should be killed and eaten or killed and fed to the dogs/buried/etc. BOSS and chick treat shouldn't be anywhere near unhealthy young birds and certainly not loads of high powered medicines either. At this point they need to develop their own immunities and they need optimal nutrition to do so...not treats. If you had a malnourished young human would you include candy in their diet?
Never give a med unless you are sure the animal HAS the need for it....if you want to take fecal samples and have them analyzed(or otherwise waste your money and time)then do so, then treat accordingly if treating your flock for intestinal parasites is going to be part of your husbandry methods. If not, then wait and see how the flock does on good nutrition and time, good management and culling the inferior specimens. If you want a strong flock out of the mess you bought, the only way to identify the strong members will be those who are given the normal, good care~this does not include drowning them in meds~and thrive on that care. Those that do not thrive on normal, good care are the ones you should remove...these will never make really good chickens that will produce for years to come. Yes, there are always exceptions but who wants to gamble on that?
Time, sunshine, fresh water and good, healthy nutrition and husbandry is enough for any flock....the ones that do not do well with that level of care are not worth your time.
As a rule of thumb for the future~if you are feeling overwhelmed while taking care of chickens, you either need to get rid of chickens and never try it again or settle down, take a breath and realize you are dealing with chickens....merely chickens. It's not Life in the ER or any other melodrama...it's merely chickens and they are tough, resilient animals or they are animals that die easily~either way you have little control over that. What you cannot control needs to be let go....chickens are for food, enjoyment, fun, etc...if you are feeling stressed then the chickens are not good for your life and need to go.
It's relatively simple.....sit down, go the beginning of the thread, read, drink a cold beverage, settle in and learn from some folks who can teach you how to not feel "overwhelmed" or make you feel panicky over your chicken purchase and new interest.,
A Newbie has found herself in trouble, merely because she is a Newbie to chickens, and you choose to chastize her,after the fact , for her ignorance in buying auction birds. I do not think she should be punished further by watching these obviously already mistreated birds die off due to a laissez faire attitude on this thread, when she has asked for help. What a "welcome to poultry keeping" idea that is!
You assume that these are inferior birds just because she bought them at an auction. It is rare, but possible to buy very nice birds sometimes, if you are not a Newbie, and know what you are looking at. I know as I had to get my start in Silkies from auctions and traders' rows.
I am in full agreement in culling weakly chickens that have had access to Normal good care, good nutrition, fresh air and sunshine.These birds did NOT, but they now have an owner who wants to help them out. What is the sin in that? We see abused and malnourished dogs every day at our Shelter, who through no fault of their own, have been dumped in horrible condition. Many go to owners who will treat them, and become lovely, long lived dogs.
There is a difference in philosophy here. I will try to help any critter who needs it, barring varmits, whom I will help to heaven.