Insulating the screen will help reflect some of the heat back into the cage, and also help keep some of the humidity in. You may also want to try and insulate 3 sides of the cage as well.

That seems like a lot heating pads to not be at the right temps. How cold is the room and how think is your substrate? What bedding are you using? And just to double check, what type of thermometer are you measuring with?

Congrats on the new snakes, and even more for already separating them.