you say the vents are bleeding, have they been hurt, picked? is their poop bloody. My first thought goes to Cocci. even if it is not cocci it is good to have the medicine anyway and it is pretty harmless.
Go to First state vet
http://firststatevetsupply.com/ and get some liquid Amprol (you will be putting it in their water) it blocks vitamin B I believe and that is what the cocci need to live in the chickens body.
In the meantime (and this is helpful no matter what the problem is) make a probiotic mash with 1 part feed 1 part real live culture yogurt, some shredded apple, and some buttermilk mix all together till like oatmeal. Put in a bowl and sprinkle with their favorite treat (scratch, cracked corn whatever) while they are watching to draw them to eat it.
In addition put food grade DE in their food and powdered milk in their feed as well.
If it is cocci this will help them out until the Amprol Arrives if not these things will also help and certainly will not hurt.
Cocci is very common and all birds have some but some need a little help developing an immunity to it and during that time they get overwhelmed and it can make them very sick, poop blood, and be lethargic, fluffed up and die quickly after that.
Also any other symptoms would be helpful.