Hi
Mine are like yours and will eat most things ha ha. However, I would be tempted to leave the treats until later in the day to ensure they fill up on layers first. Perhaps even crush a bit of shell into it to help. If they are all having soft shell issues it might be worth a try.
Hope...
OMG! -10 celsius! I am learning so much about chickens and how hardy they are from you all.
I panic if it's minus 2 celsius overnight ha ha. I make them a warm breakfast of layers and porridge tee hee.
I agrree Microchick-olive oil is wonderful. I add it to their scrambled eggs.
My girls love: tuna, prawns, ham, bread, spinach, porridge, cat food - in fact anything ha ha.
Here is Sofia staring Eddie out after getting into the kitchen and eating my cats' food ha ha.