I've always been told you cant really overfeed unless they are meat birds that are bred to be heavyweights but are being kept long-term as pets. I wouldnt expect it to be a problem with layers, everyone lets them eat as much as they want.
You mentioned the cold.. Could it be that their water is frozen and they are dehydrated, causing eggbinding and vent problems, which led to the bloodthirsty behavior?
Sorry I wasn't more helpful. Do you have any idea what could be causing your recent problems? Could your birds be overcrowded or unhappy for any reason? Do they have access to feed and water all day long? Have you examined the vents of the whole flock? It seems like the bloody eggs and the vent...
You should try to be more specific. Do they look like they have obvious injuries, or just unexplained blood? Could they have been attacked or are they sick?
from your picture and your description it seems like they will be fine
i almost suggested adding an awning above the three large windows, but it looks like they are glass or plastic, not hardware cloth, so snow couldn't blow in anyway