I was a wildland firefighter on a Type 1 (smokejumpers/hotshots and the like) for 10 years. You have NO idea how hot that fire will be if it comes your way, and it could (or might not be too) be so hot that you AND your chickens won't survive, even if YOUR area is cleared of fuels. If the fire has 300 foot flamelengths and your property is in its path as it moves past, it will be too hot for you to "weather the [fire]storm". You might get away with it in a basement, but I wouldn't put my animals or myself at risk of that, and its unfair to put the firefighters at risk should they find out you're in there and attempt to rescue you. Please, please, please leave if you are asked to do so, and take your chickens with you, if at all possible.
Do you have a truck with a topper, by any chance? We transported our chickens in a pretty small kennel, when we bought them. They weren't happy about it, but they came out okay. Good luck, and I'm so sorry you have to go through this. I've seen my fair share of pet deaths and burned up homes, and I hate the thought of it happening, ever.