Also do you have a different waterer than the one i see in the pic?
They really NEED a waterer that is deep enough to keep their nose clean and dunk their heads in to clean eyes as well.
Search duck waterers on this forum if you need some different ideas.
Some people use milk jugs and similar...
Of that container they are in has no ventilation in the sides thats why they are getting too hot.
Can you get them moved into something much larger and open?
I brooded mine in the coop outside. And by this age they were already staying pretty far from the heat lamp. And on then outside edges it...