BPs are terrestrial snakes. Measuring your temps at the top of your cage does them no good. Ambients should be measured near the bottom of the cage. You want your hot spot thermometerprobe on the bottom of the tank, preferably under their hide. I hot glue mine down and don't usually have a problem with my girl pulling them off (She's the only one not in a rack ATM, just a tub). You want your thermostat probe between the UTH and the tank glass. I don't have any experience with heat lamps of any kind so I'm no use there, but I can help you get your UTH situation under control.
And don't worry about the one that hasn't eaten since October. It's breeding season and they're adult males. A lot go off feed this time of the year.