I'm using a Sunbeam extra large heating pad because I can turn off the auto-off feature and it has number for controls rather than high, medium and low. I set it on 6 to start with and then watch the chicks' behavior to see if they are doing well. I didn't realize that some of your chicks were that old and others much younger. I'm not sure this system is going to work for them. That age difference doesn't seem like much until they hit that 4-6 week old or so stage...then the differences can be pronounced both in feathering and in size. The heat requirements change as they grow - think of the recommendation to start the temp in a brooder at 95 degrees, then lower it by 5 degrees each week when you use a lamp. That can't be done as easily with the cave when the chicks are different sizes. If you really want to do this, then I imagine you'll need a little trial and error to find a modification that works for you. If not, well, spring is almost here and yours are growing up fast, so if you can just get through a couple more weeks you should be golden. Sorry I couldn't be more help.