You mention that you are having issues with 3 of your reds (what are the issues?), but it's affecting the BO's.
Are ALL of them having combs turning black.
ALL are having yolky poop?
I'm sorry your BO does not look well at all. Where are you located in the world?
Photos of poop may be helpful.
Let us know what her crop feels like, if she has a sour smell to her breath. Any lesions, sores or canker inside the beak. Feel her abdomen for bloat/swelling or fluid. When is the last time she laid an egg?
Sorry for all the questions, but trying to gather more info - if ALL are like this, then think about whether they got into something rotten or toxic.
Have you wormed your flock - do you have a vet that can run a fecal float to look for worms?