I'm sorry he is not doing well.
Can you take him to a vet?
Does the crusty stuff stink?
The crusty "stuff" on the beak - look inside his beak as well - do you see any more inside or what might look like yellow plaques or lesions?
I'm not a vet, nor an expert, but my first thoughts is Canker. Which can be difficult to treat. The green poop, I would be inclined indicates infection and maybe not eating well.
You can try treating with Metronidazole (Fish zole/Flagyl) at 25 mg per pound given twice a day for 5 days.
A vet could verify Canker or some other condition. Canker (Trichomoniasis) is a protozoan infection which is highly contagious, so keep him separated. If the other one is showing symptoms, separate her out too - but you will want to keep them apart to help prevent spread. Shared water and feed bowls need to be cleaned and disinfected. (all containers that your flock has used)
Some people do recommend using Acidified Copper Sulfate (order online at places like jeffers pet) to help prevent spread of infection to other birds. You do need to read and follow packaging instructions for Acidified Copper Sulfate - it needs to be pretty precise in dosage and time given. Usually it's 1/4tsp per gallon of water given 3days a month.(only use plastic/non metal water containers with Acidified Copper Sulfate)
Do your best to keep him hydrated - birds with Canker can have a difficult time eating/drinking. He may do better with feed made into a wet mash.
fwiw- he benefit would from eating a higher protein feed like chick starter or flock raiser. The Dumor Grower/Finisher is only 15%protein, which, imho is low for chickens. Scratch is very low, usually around 8%, so this further dilutes nutritional and protein intake.