You'll need to sort out alternative arrangements soon as I believe you now have another batch of eggs in the incubator. The new chicks you hope to hatch won't be able to join the ones you have at the moment, as the age difference will be too great. How old are the first lot now? If you've been gradually reducing the temperature in the brooder, I'd imagine that at this time of year they would normally be well enough feathered to go outside during the day in a small run on grass, with a waterproof cover over the top. They'd certainly benefit from this immensely, and would be OK brought in to an unheated brooder box overnight, without extra light.