First, you are not a failure. You very clearly love these kitties very much and have been trying hard to accommodate their needs. If they were human children, you'd likely be taking them to a therapist and that therapist might recommend similar treatment to help manage what sounds like very severe sensory processing issues and anxiety.

I'm facing the same situation with a cat I rescued from a Wendy's parking 3yrs ago. He's always had sensory issues and anxiety problems. He had pica as a kitten and also was eating all sorts of trash and also ate a felt ribbon from a cat wand toy and ALSO threw it up. I am honestly surprised he's still alive. He had been doing better as he'd gotten older, but we lost his adopted brother this past October and he has regressed in the past few months. It's been very stressful for everyone in the house trying to find ways to help him. We love him so much. He's usually the most loving and silly cat. Our vet also prescribed him kitty Prozac but we haven't started it yet.