They look like burns to me. I've noticed you posted about this earlier, and another previous post about scale rot or a burn. There have been numerous people asking you about your heat source, which you've stated a heat pad, and people asking if you are using a thermostat, but you have yet to answer that question. I don't want to ASSume anything, but I'm going to guess that you aren't using a thermostat and for how long now your snakes have these "scale rot/burns" on their bellies. Again, I am not trying to ASSume anything, but I can't help but to think that this is what's going on.