I dont know how sensitive angels are to temps, but I found lowering the temp to around 76 (because heat induces the bloat process), adding epsom salt (to help them clean their bowels of blockage) and only feeding them spirulina based foods (algae) have helped me in the past. No Protein based foods at all if possible. Check the labels for contents.
Bad news is that once it gets to a certain point, its almost irreversible. Most of the time, its caused by stress, in my experience. I just lost 3 ex-cichlisoma Istlanum because the single male stressed the other 3 so bad they got bloat.
Some fish are prone to it, but I have never heard angels were. Has anything stressful happened in or near the tank? Have you checked for stray voltage from the heater or filter?
Si vis pacem, para bellum