get it to the vet. you may have a problem.
This doesn't sound good i'm afraid. There is a strong possibility from the symptoms you have described that your birds are infected with an organism called Salmonella gallinarum (or possibly other strains of Salmonella), these bacteria are excreted by wild birds, which is usually how free range poultry contract the disease.
All the symptoms fit, as most parasitic diarrheas (caused by worms or protozoa) cause blood and mucus to be excreted as well.
It may be possible to treat the birds with antibiotics, but sadly, even if cured they often become carriers of the disease- so any other birds you get will become infected- you may actually be better starting from scratch (which as a fellow poultry owner i feel very sad in having to recommend).
Sorry not to be more positive- but very often the best way with nasty infections with poultry is to clear out and start again.
If you go down the line of treating these birds with antibiotics- i would wait until these birds are gone before restocking.
ive never had this but its what an ex bat should have been treated with. its to quick for worms so until proven otherwise assume the worst.