They should be just fine. But make sure you have enough ventilation and no drafts. If you’re still worried and want to use heat absolutely do not use a heat lamp! Huge fire risk. Instead use a plate/contact heater. I only have 3 birds atm, so I have some plate heaters in the coop with them. Do they need them at 25F probably not, but it’ll sure make me feel better tonight when it gets down to single digits. I do think folks underestimate the stress bodies go through at extreme temperatures. When it gets to single digits maybe and definitely negatives I think you’re running the risk of stressing the birds and they’re vulnerable to sickness. Another quick note, I think a steady trend down in temps is less risky than if you have a sudden cold snap where it jumps down several dozen degrees.