"Who's responsible for the hallucinations?"
Only one possible answer : the entity whose name is on the document. If it's a website, the owner of the website.
Stop splitting hairs in two. If a company builds a false-facts-spewing tool and makes it available, the company is responsible for the fallout. If I buy a second-hand vehicle and cause an accident, I can't go say it's the previous owner's fault. Companies that build these hallucinating tools should be responsible for the hallucinations.
Maybe, once the company has been dragged to court and found guilty, it can then turn and slap a lawsuit on the company that built the drunken slob for it, but it's the company that is using the tool that is responsible.
What about someone who uses such a tool to make legal documents for personal situations ? Well don't, first of all. Go get a lawyer to do the job. Second, the individual used a website, so he can attack the owner of the website.
Responsibility is simple in this case. Except for the obvious fact that companies will be dragging their feet as hard as they can, and lobbying like mad to get out of paying for any damages - as they have always done. But that doesn't last. Even the tobacco industry has had to bow in the end. Bil Oil will too, some day. Let's not start messing around with Big AI without laying down the ground rules firmly.