Realistically until you can stock some instant heat packs the best thing you can do is move the snakes into the warmest room of the house, making sure they are well away from outside walls and drafty windows. You can cover their enclosures with a blanket to retain the heat in there as long as possible. However, you MUST make sure that they can still get some ventilation and you MUST make sure your heating source will not be in direction contact with a blanket.

If all else fails and it's getting too cold, heck put the snakes into small escape proof containers (ventilated) and get under some heavy blankets with them. Your body heat trapped under blankets will help somewhat until your mom can get some heat packs. It's always best to have some of them on hand if you live in an area that gets hit hard.