I think Twitter is owned by a holding company controlled by Musk. I think he had at least two holding companies, “X Holdings I” and “X Holdings II”, with the later a subsidiary of the former, and the acquisition was legally a merger between Twitter and the subsidiary. That’s a quite typical way to legally structure acquisitions.

I’m not sure exactly how the coinvestors fit in the picture, but I expect they (or more likely their own holding companies) own minority stakes in the parent holding company. The debt is probably the parent company’s also, although Musk may have personally guaranteed much of it.

Also, probably even the parent holding company is not directly owned by Musk. Probably owned by one or more trusts he controls.