Hatching Fever,
It sounds to me like you just don't know what you're doing and I don't mean that to sound condescending. We were all new to raising them at the beginning. There is no reason at this point to assume you were sent sick birds or even that they are "sick" other than stressed. Here are some basics:
#1 You should "Never" put new birds anywhere near the others for about a month for quarantine and watch for signs of illness to treat quickly.
#2 "Never" feed what you have been feeding to a chick or young bird. That's enough to kill them right there. There is a reason they call it chick starter and grower and even that should be pulverized a bit more for these little Serama's.
#3 "Never" give gatorade to them. That is not a balanced electrolyte for birds and can kill them.
#4 "Never" stack cages so there are droppings falling into the others cage, even if they are your established flock. If you need to stack the cages, there should be a barrier of some sort, even a piece of cardboard that can be thrown away when dirty.
DO:
#1 Always have a clean, quiet, warm, safe place for new birds set up "before" they are to arrive that is as far away as possible from your others. When ready to join the rest of the flock, be aware if you add new ones to an established flock, there may be fighting and injury even with hens. I've found night time is a better time to integrate them and I try to never just put one newbie in a pen, at least 2 together that are bonded will be less stressful. If you only have one newbie, then take one from the established flock and pen it with the newbie till they bond before adding them back into the flock. You might have to try a couple different ones to find a good match personality wise. I find this a lot less stressful to them all.
#2 Know in advance what they have been eating and have it on hand and if it's not available in your area, then ask the breeder to send some with the birds or find out where to buy it online. Feed "Appropriate" food. You don't give scratch or grains to "any" chickens on wire unless they have free access to grit/gravel. You also do not give laying mash or pellets to young birds. They should get grower until they are laying, the reason is because of the formulation, the added calcium and other things in laying feeds are not made for young birds and can cause problems and they will be shorter lived. Add the new feed and make sure they aren't just eating the other stuff before you feed only the new feed.
#3 Always wash thoroughly before feeding, handling or cleaning before going back and forth between the new guys and the home flock. It doesn't hurt to keep a pump bottle of hand sanitizer be the pens for use between handling birds.
#4 On arrival, give fresh water with a "poultry electrolye" solution only and the feed they're used to. Give them a few days to settle in and just don't handle them a lot. That is stressful too. The electrolytes help with dehydration from a days travel with no water. After they are drinking good, plain water is best. If you are feeding what you are supposed to be feeding, you should not need or add any other supplements like extra vitamins. The key is "balance" and adding a vitamin solution can throw the balance off and cause health issues like kidney and liver damage.
#5 You should have emergency supplies on hand already. It always seems like if something is going to happen, it's going to be after hours and weekends, especially holidays, lol. With birds, they don't show illness until they are really sick so treatment needs to be rapid. Keep a small variety of antibiotics on hand, know what they are and how to safely use them.
#6 Learn the basics of illness in chickens and learn "prevention". Rushing to treat with a bunch of antibiotics if they aren't needing them can also kill them by knocking out the good bacteria they need in their body to function. Once antibiotics are given, give them some probiotics (for livestock, I use the powder and mix it with the chick starter when I put it in my Silver Bullet to grind it). Probiotics won't "cure" a disease or illness but it helps them to digest and process their food better and that will help with stress.
#7 Worms are not an emergency. Any chickens on the ground or access to veggies (a great way to give them worms) will have worms at some time in their life. Treating them with DE is fine and safe but some of the more harsh type chemical wormers can kill if they already have an overload of worms so always start with something safer like the DE and Piperzine. Then give probiotics and a few weeks later give them a stronger wormer like Panacur or Ivermectin if there is "proof" that they are still wormy.
#8 Lice and mites are another reason to quarantine new birds. Dust them and the cage with Sevin and spray the vent area with WD-40 and let it go for a week or so and when they are settled in, you can give them a bath and inspect them and "IF" they still have some bugs, then clean the cage good and treat again with a drop or two of Ivermectin pour on to the skin on the back but I'm betting it wouldn't be needed.
#9 I Know I am forgetting some things. It's pretty basic to me because I have been in health care for 30+ yrs plus I've had pets and animals for longer than that but even with all that, I learn something new everyday. Groups like this are a treasure chest of information but please don't take anyone's word, find yourself a really good book on poultry health and care and consider all the things others tell you but be aware that some are not always right on correct. Don't panic, learn to "observe" your birds and you'll be amazed how you start noticing things about their personality, health, etc and you will catch on quickly then, when any of them are not acting right. The signs of a bird in distress is very subtle, tiny changes shouldn't cause a panic, just be watchful and ready to act as "needed".
Best of luck
Cathy
Cathy