Poor guy!
Check both roosters again to make sure they don't have any additional wounds that are hidden under all their feathers.
The wound on your rooster, I'd try cleaning it again, trim some of the feathers away from his wound so it's easier to see and tend to.
If you have Hibiclens...
I'm sorry they are not doing well.
Photos of both roosters would be a good idea.
Were they fighting?
I'd try to get some poultry food as soon as possible, get them hydrated and eating. Electrolytes for a couple of days would be good.
Fwiw - The Gizzard is part of the digestive system and...
Welcome To BYC
Can you post photos of him and his poop?
Did the feed get moldy when it washed out?
Take him aside, offer him electrolytes and some wet soupy feed. Examine him for lice/mites, tell us what his crop feels like too.
Have you ever dewormed him?
More information like his age...