If the eggs are pipped (when the keet has cracked the shell and has began the process of hatching), then I'd stop candling them and leave the incubator closed so they can hatch... every time you open the incubator you draw the humid warm air out and let in dry cool air, which causes the inner membrane to shrink down over the keets. That will make it difficult or impossible for the keets to hatch. When that membrane ends up shrunk/sucked down over the keets they are stuck in place and cannot spin around inside the egg and zip the shell... they end up struggling too long and expire from all the effort.
As for the one that died, sometimes they hit a vein when they try to pip, and they bleed out and die... but he may have some kind of deformity (from your temp being so far off) that prevented him from effectively zipping the egg too... possibly cross beaked or something. I'd wait until the hatch is over and then open up that egg to see if you can tell what happened (if you can stomach that, and want to know what might have happened). Unfortunately, due to the late hatch you might lose quite a few keets... they very well could have deformities from the temp being off or fluctuating too much. I'd definitely double check your temp before you set any eggs in that incubator again, ugh.
I'm crossing my fingers for you that you at least get a couple healthy keets out of all of this