Hello Phil:
There's a lot going on in there for you.
Before I begin, I just thought I'd share an opinion with you. That opinion is, there is no justification for bringing harm to another human being, including yourself. I was glad to read that you were wise enough within yourself to recognize that and shouted out "NO!" when instructed to do so by that voice. That takes a lot of strength and tells me that you are intrinsically a compassionate human being who is concerned for yourself and others.
Part of your experience reminds me of another fellow I spoke with who also had some troubling voices in his head. I shared the following activity with him and he found it to be a soothing exercise. I share it with you in the hopes that you may also find it helpful, but I don't know for sure if you will. You decide...
This is an imaginative exercise in which you construct a mandala structure. If you don't know what that looks like, you could check out this page from google:
Mandala Images. Anyway, this is how you do the exercise...
Imagine a large square. Into each corner of the square place a protector. The protector can be someone you know from real life or it may be an imaginary figure -- the important thing is that you trust this "protector", you feel safe with them, and you feel loved by them. They are on your side. Next, you are going to imagine a circle within the square -- place yourself within the middle of the circle. You are safe here, surrounded by your protectors.
It wouldn't surprise me if Otis didn't like this idea. If he gets lippy with you, I suggest you let one of your protectors deal with him. The plain and simple matter is that Otis is not allowed to harm you and he should know better. The same goes for Plabius.
This is a very simple exercise that
may bring you a sense of comfort. I can't say for sure if it will because I'm not you. I suggest you try it and if it helps, keep doing it. If it doesn't help, that's just because it doesn't.
Please feel free to share that exercise with your therapist and your parents. I wouldn't want you to feel there's anything I (or anything anyone else might say) that you should keep secret.
Best of luck to you Phil.