I'm so sorry to hear about your roosters. It sounds like you're dealing with a serious issue, especially with multiple roosters showing similar symptoms. The purple comb, lethargy, and tail position suggest that there could be several things going on. Here are a few things to consider:
Coccidiosis: You've already started treating for coccidiosis with Corid, which is a good first step, but keep in mind that it can take several days to see improvement. Make sure the water is fresh, and if you're treating for it, continue the Corid treatment for the full 5-7 days, as per the instructions on the product. Monitor them for signs of improvement.
Respiratory Infection: The lethargy, quietness, and purple comb could indicate a respiratory issue like Mycoplasma (MG), ILT, or Infectious Bronchitis. These infections can spread quickly, especially in flocks. You should monitor for other symptoms like nasal discharge, coughing, or swelling around the eyes. If you suspect a respiratory infection, you may need to consult a vet for antibiotics or other treatments.
Poisoning or Toxins: If there is anything toxic in their environment (plants, chemicals, contaminated food, etc.), this could lead to similar symptoms. You've already sanitized the coop, which is great, but make sure there's no source of toxins they could have accessed.
Nutritional Deficiencies: Ensure they are getting proper nutrition, especially in terms of vitamins and minerals. You've given Nutra Drench, which is good for a quick nutrient boost, but also check their regular feed to ensure it's balanced.
Predation/Stress: Sometimes, roosters can get stressed due to changes in the environment or the presence of predators, which can cause them to act strangely and even become lethargic. If they are under any stress, try to minimize it.
For the rooster that is currently showing symptoms, continue the isolation, Corid treatment, egg yolk, and Nutra Drench. Make sure he has access to fresh water and food, and keep him as comfortable as possible. If he doesn't improve in the next 24-48 hours or worsens, it might be time to consult a vet, especially if a respiratory infection is suspected.
I hope he pulls through! Let me know if you need anything else.