If your chickens have cocci it is not a big deal. If you catch it early it can be treated quite well with Corid. Chickens with cocci though usually (but not ALWAYS) have bloody poop (fresh red blood, not intestinal lining) They are also usually listless and puffed up. Like a previous poster said you do not have to cull your entire flock if they have cocci. It is not that big of a deal if you get the meds into them quickly.
That said, I don't think you have cocci. I would do a serious and fast search on Mareks. The one leg up and one back is classic and chickens usually die quite rapidly. Death rates are very high. If you haven't already isolated each one at the FIRST sign of symptoms you need to start doing that right away. Sounds like you may have another one???
Show your hubby the picture of Mareks posture that you will find on here or any google search. There is no treatment for Mareks although some birds do survive. The only way to positively diagnose is necropsy. There are 4 kinds of Mareks, all caused by a virus. The one that does that to the legs is the neurological kind. At necropsy the vet would find lots of small tumors in the organs and spinal cord. The legs do that because the sciatic nerve is affected.
Don't put the Welsummers out with the others until you know exactly what is going on. They can handle being lonely a few days. I can't remember if you can eat the eggs if they have Mareks but I wouldn't. Cocci is in the soil. It is spread by regular birds. All chickens have it, they just build up an immunity. baby chicks eat their mom's poop to do this. Cocci symptoms occur when the protozoa overwhelms the bird. You don't need to cull a whole flock for cocci. But you may want to with Mareks.
Sorry, I just read through the thread again, and you have a third chicken down. Antibiotics won't help with Mareks or cocci. I wouldn't give them anything until you know what is going on. Especially human meds.
I'm so sorry. I really feel for you but keep whoever is still isolated--isolated.