I haven't tested this out, but my tentative plan is to bag the snakes and put all the adults in one tub and all the babies in the other. I'll put a layer of hand warmers down then a double-thick towel over them to prevent burns and throw everyone on top of the towel and close the lid.
Don't use hand warmers in a closed container. They use oxygen to heat and it will take all the air out of the container and then the snakes will not be able to breathe.
0.1 Lesser
1.1 Pastel
0.1 Black Pastel
0.1.1 Normal