@birdman55,
You are getting the first real winter for a long time. Part of challenge is a function of species / breed / strain selection. Events like this are what leave only the stronger birds to carry forward the gene pool. It is a form of selection.
Stock types you have are your business.
When it comes to use of hays, I suggest you use straw instead and leave some in square bale form. Birds can get up off ground even if inclined to roost on ground. My birds will stay off ground for days when it gets really cold. I then apply feed to top of hay bales.
Check weight of your birds. When it gets really cold, the birds have a tough time keeping weight on. Shorter day length makes for longer interval overnight where crop is depleted without energy for staying warm extracted from food. Then they must tap into fat reserves. Small under weight birds may not even be able to process food fast enough to maintain full body temperature.
You are where you can throw out door the old wives tail about how evil corn is for games. Pop it too them when it get really cold. Not nutritionally balanced but it is energy dense and they will eat a lot of it even after topped of with whatever ground feed mix you are using. Feeding with intact grains also may help reduce need to liquid water. Make some of those feeding blocks so birds can pick feed off at leisure without venturing away from cover.
Growing up, I was ingrained with concept you do not waist pen space on chickens hatched later than June 1. Winter time discussions explained that as economics where the younger birds seldom matured enough to pit that first season. The younger birds also did not have the body mass or feathering needed to resist intense cold. I do remember winters in the 1970's where young birds and those in poor health suffered significant deathloss and very much more prone to frostbite. Because of the challenges, we where very much against getting stock from deep south because they could not handle harsh winters as well.
We could raise chicks in barn during even worst of those winters but great effort had to be invested in keeping everyone dry and protected from wind.