Adjust your heat lamp till the temperature reads 90 degrees on a thermometer when you lay it directly in the bottom of the brooder. Temp should not change in a 2 hour period. Keep raising the lamp until the temp is correct. But keep checking temp for them 2 hours every 10 minutes or so to make sure the temperature is not climbing higher. You need a large enough area that the chick can escape the heated area if they get to warm. Move the water and food closer to the middle of the brooder so the chicks can get to it. You may want to give the chicks also some electrolytes to help them. Boil a quart of water mix in 1/2 cup of sugar, 2 teaspoons of baking soda and let it cool. You may have to use your fingers and put a drop of water on its beak a few times every hour or so till its eating and drinking on its own. Also mashed up egg yoke, just a tiny bit at a time.
Once temps are corrected and everything is ok drop temps by 5 degrees each week.