When I started out I just had 3 rsl hens in a metal shed.They did fine.Next year I had 2 rsl hens and 5 ee hens.They did fine too.This winter I have a roo,1 rsl hen,and 5 ee hens. I bet they will be ok.No heater. I just added some bales of straw to line some of the walls.I do have a problem with the one rsl hen sitting in the boda nest box which is a domed cat litter box. I think yours will be ok even the one with the sweater. Maybe only an issue if one hen sits all alone.Look for frostbite.We never had it.Maybe give scratch before bed.
I did add a light last weekend due to no eggs,but it provides no heat at all.In our area we get down to the single digits. I take out hot water.Oh, that reminds me the first year when I had 3 I would take out gallon water jugs filled with hot water.Morning and night time I put hot jugs in.Don't know if that was helpful for the 3.