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Being on the camera at the same time, or at least in the same conversation, makes it Talking To Himself. Otherwise, just a single actor playing multiple roles is Loads and Loads of Roles.
Firstly, I'm not sure where you get the idea that "examples that are actually live actors" wouldn't count as examples of Talking To Himself. The trope page has an entire paragraph about that, which cites a live action film as an illustration.
Secondly, it's not an either-or thing; Talking To Himself and Loads And Loads Of Characters are two separate tropes with different criteria that sometimes overlap and sometimes don't. If an actor plays loads of characters and at least two of those characters have a conversation, that's an example of both tropes. If the two characters who hold a conversation are the only two characters the actor plays, that's TTH but not LALOR. If an actor plays loads of characters but they're never shown to interact, that's LALOR but not TTH.

Talking To Himself (especially its subpage for Live Action Film) seem to have a lot of examples that are actually live actors. I would just remove them, but there's so many I wondered if there are subtle distinctions that mean they don't qualify for Loads and Loads of Roles. Is it because the actors don't actually appear on camera at the same time?