First, they have no identity from each other. We know Laman is the older of the two. That's about it. They seem to act mostly (but not always) as a single unit. They change their minds about whether or not they believe the religious preaching of Lehi and Nephi at the same times. They abuse or attempt to kill their brother at the same times. Not once does Lemuel tie Nephi up and Laman plead for his release. They act in unison. They probably braided each other's hair too.
Second, I have never met a single person who is quite so fickle as these two clowns are. Let's run through their waffling so far:
- Laman and Lemuel beat up Sam and Nephi for nearly getting everyone killed trying to get the plates from Laban.
- A freaking angel of God appears and tells them to cut it out. They cut it out.
- After retrieving Ishmael's family from Jerusalem, Laman and Lemuel rebel against Nephi and tie him up with the intent of leaving him to die.
- After Nephi escapes his bonds, Laman and Lemuel are apologetic and even go so far as to pray to God for forgiveness.
They change their minds all the time. And when they do, Nephi usually swears by it. He calls them "humbled" or something to indicate that, yeah, that sudden conversion was for real. Even though they were murderously angry a few verses ago, now they're true-believers.
Their waffling continues when, in chapter 15, Laman and Lemuel say they haven't prayed for understanding of Lehi's dream because God doesn't talk to them. Nephi then goes off on a rant about how hardhearted they are and apparently he explained just about everything to them. Their response?
These two guys who have beaten Nephi up, tried to kill him, and will later try to kill him again, start asking questions about Lehi's vision. And not just basic questions like "What does the iron rod represent?" They ask perceptive questions, too, such as verse 31, which is along the lines of: "You said the chasm between the righteous and the wicked represents hell...does that refer to temporal suffering in this life or does it refer to the suffering of the soul after death?"
That's kind of weird. They're asking detailed doctrinal questions like that when their only apparent motives so far have been:
- Stay in Jerusalem because home is awesome.
- Don't get killed.
- Get Nephi to shut the hell up.
They don't care about their dad's visions or their uppity younger brother's soapbox. They don't think Jerusalem is going to be destroyed and they don't want to wander around in the desert for years. Considering their desires and concerns are almost entirely about whether they'll be able to chill at home not giving a crap about anything, why would we believe that these two are busting out with the Sunday-School-discussion-generating questions?
So, to summarize: Laman and Lemuel are interchangeable, unrealistically fickle, and do things that aren't supported by any of their motivations. That, to me, is plenty of support for the theory that they are not, in fact, historical figures. They are poorly written one-dimensional fictional characters.