I'm not sure what happened with my cactus. I have it indoors and its been doing fine for a little over a year. I keep it on a shelf with my moon cactus (I think these names are right) and I noticed what I think was mold on my moon cactus's pot and soil. I cleaned up the pot and soil and its fine now. But then I was looking to make sure it didn't spread to my other cactus and I noticed a cobbwebb like spot in it. I've also noticed a brown spot. My boyfriend suggested that as far as the brown spot maybe I have too many little things branching off and I should cut some off? I'm not sure . but I'm worried that the cobbwebb part is mold or something. Does anyone know what this is? Thank you in advance!

***you have to look super hard in the second picture I apologize my camera sucks.***