The heat mat won't raise the ambient. Your thermometer probe should be over the hot spot and you need to adjust your thermostat until your thermometer reads the correct temperature. If the heat mats don't have the same wattage, you're going to need two thermostats or the same wattage heat mat. Otherwise you're going to get different temps. The mat should cover at least 1/3 but not more than 1/2 of the bottom of the tub to be able to provide a proper thermal gradient for the snakes.

77 is okay for an ambient. 78-80 is better, but 77 will be okay. The heat mat won't raise the ambient, you're going to need to use a warmer room or put a heater in the room with the tubs.

110 is a temp that would be expected out of an unregulated heat mat and a snake laying against that will be burned. You don't need to worry about either of your snakes being subjected to a burn after everything else you're dealing with.