If they are in about the same conditions and their temps are the same when you measure, one thermostat should be fine. I have one strip of heat tape for 9 snakes all plugged into the same thermostat.

I use tubs, too. You may want to put the female into the bigger tub since she will probably grow to be larger than the males. Make sure to poke a few holes into the tubs for ventilation and you will have to make sure the snakes can't get out somehow (BPs can pop lids open easily).