I didn't really interpret that as Sirius mixing up Harry and James in any meaningful way.
If this were real life, I'd agree; I call my kids by each other's names all the time, but this isn't real life. They deliberately wrote that slip of the tongue into the movie script although there was no similar slip anywhere in the novel. I can only interpret that the screenwriters agreed with Molly that Sirius sometimes forgot that Harry wasn't James. I, however, do not agree and resent that they wrote it in.
And yes, Regulus is RAB. Of that, I am 100% certain.
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If this were real life, I'd agree; I call my kids by each other's names all the time, but this isn't real life. They deliberately wrote that slip of the tongue into the movie script although there was no similar slip anywhere in the novel. I can only interpret that the screenwriters agreed with Molly that Sirius sometimes forgot that Harry wasn't James. I, however, do not agree and resent that they wrote it in.
And yes, Regulus is RAB. Of that, I am 100% certain.