Hi Rose,
Yes, OT 4, 5 and the rest of the OT levels deal with BTs in some way or another.
I don't know of any other spiritual group that believes we are composed of beings. Scientists say we are composed of cells and living tissue, not living beings.
Exorcism is about demon possession. Demons are non-human mythological creatures that supposedly exist to torture us.
There are no explanations for BTs, what they really are, where they come from or what their purpose is. BTs are part of an incomplete, half-ass sci-fi story that L Ron Hubbard tells Scientologists on OT3, the Xenu story. That's all Hubbard ever tells about them, and that's pretty lame, especially for an experienced sci-fi writer.

He doesn't call them human spirits, but leads us to believe they are, but maybe they're not, but maybe not all, but maybe something else.

If they are actually spirits that were all stuck together from an explosion, then why do we treat them like they are some sort of degraded, lesser thing and call them BTs, instead of just thetans or spirits? It's just weird.

Part of the whole confusion that is the glue that makes people in Scientology want to find out more, spend more and traps them into the con that Hubbard designed.
I think L Ron intentionally didn't describe them more so that others would envision them their own way and by doing so, participate in the scam. Agreement and envisioning...key factors in hypnotism.