AWWWWW! Those chicks look so sweet. Your set up looks fantastic to me. In the spring my broody did fine when our night temps dropped to 25-35'F (but daytime temps went back up to 35-45'F). I never had to add heat, but I did have to chip ice 2-3 mornings. The chicks would dash out & then back under mama. I personally never had chicks in the roughest part of winter, but a few people in our area have. The temps dipped to -40'F at night during a polar vortex, & their broody hen was still able to hatch some eggs.