The thing that's always puzzled me about the Mahabharat is why Nakul and Sahadev are in there. I mean, it's not like they actually do anything. My knowledge of the epic is admittedly sketchy, but as far as I can remember they never kill anyone important or say anything profound. They're as useless as a client team on a consulting project. Even relative losers like this Ashwathama dude are more critical to the overall story. Nakul and Sahadev are the R2D2 of the Mahabharat, only less funny.
My conclusion thus far has always been that they're straight men, included in the story to make their older, more successful brothers look good by contrast. It wouldn't do, after all, to have all the Pandav brothers be supernaturally gifted - it would strain the veracity of the story (ok, so we're talking about an epic where children learn to execute complex military maneuvers while in their mother's womb, but never mind). So you add in Tweedledum and Tweedledee, and everyone can think about their idiot younger brothers and relate.
Thinking about it though, it occurs to me that maybe the whole point about these two is that they're not straight men. Think about it. You've got these three hulking Kunti-putras, all strong, virile young men, and not one of them has the slightest chance of ever ending up in a relationship - Bheem is a neanderthal, Yuddhishtir can't tell a lie (which means the first time she asks him how she looks it's all over) and Mr. Oh-master-I-can-only-see-the-eye-of-the-bird Arjun is precisely the kind of sleazy jerk who keeps his eyes firmly fixed at a point south of your neck. Plus which they all still live with their mother. What self-respecting woman would date guys like this?
What, then, is a sexually frustrated mythical character to do? Enter Pretty Boy 1 and Pretty Boy 2. After all, every superhero needs his sidekick. Look at Achilles. Look at Batman. It's obvious when you think about it - Nakul and Sahadev are comfort brothers - sexual paramours generously provided by Kunti to keep her sons in good fighting trim. It explains so much doesn't it? The whole house of lac thing for instance. I mean, why would you go into a house made of a substance that melted and dripped when heated unless you were looking for some serious S&M? And the whole Draupadi thing. Think of it as one woman among five men and you have to wonder how come they didn't kill each other. Think of it as three couples with a lot of partner swapping and it's happy families all over.
At this point you're probably thinking, but wait, wouldn't that be incest? For starters, notice we're talking about a bunch of people who spend pretty much their entire lives trying to kill their first cousins (an ancient Vedic tradition now sadly lost to us), so you could argue that having sex with your brother is relatively tame by comparison. More to the point, though, notice that technically Nakul and Sahadev aren't related to the other three at all. Different mother, different father(s). So no problem there.
In Vyasa's original text, as I imagine it, this role of the two 'brothers' no doubt received a lot more attention. There were probably long descriptions of the duo's special...errr...talents and steamy scenes depicting their interaction with the Kunti-putras. Later versions of the text have, obviously, censored these out (along with anything else that smacks of homosexuality ), leaving us with these anemic, mild mannered younger brothers who just don't seem to fit in. Such a shame.
 I'm unconvinced, for example, that the Bhagavad Gita is really about Arjun's reluctance to fight the Kauravas. Consider the history of Arjun and Krishna together, their closeness, the way they go around setting whole forests on fire, the alacrity with which Krishna agrees to be Arjun's 'driver'. Look at the stock picture of the scene, with Arjun kneeling awed but also hesitant in front of a Krishna who stands upright, facing him. Read all that stuff about wanting action without fruit of action. Ask yourself whether anything in Arjun's character has suggested any reluctance whatsoever to go into battle, and then think about what else Krishna might be asking him to do that he might have qualms about, especially out on an open battlefield with all his family and gurus watching. Do I really have to spell this out for you?