I can definitely imagine them having a bit of a rocky relationship.
We haven’t really seen a lot of the Dewey and Louie dynamic on screen yet. In fact, it was super hard for me to find a shot of both of them in the same frame (Confession: I had to shamelessly crop Huey out of this one). Hopefully, we’ll see more brother-bonding soon!
In the meantime, given what we do know, it’s fair to suggest that Dewey and Louie probably aren’t as close, or, if they are, their relationship with each other is a lot more turbulent than their relationship with Huey.
They are just so different.
Dewey is all about the thrill. He’s an adventure seeking, live-in-the-moment, do-it-for-the-vine kind of guy. He rarely thinks about consequences to the point that he often puts his personal safety and the safety of others at risk - LCOTSC, anyone?? Dewey is led purely on emotion and adrenaline and swagger.
Louie is exactly the opposite. His mind is always on the future, and he, better than any of the boys, understands cause-and-effect and consequences. He identifies and recognizes threats and has a healthy sense of fear. Where Dewey is all nerve and bluster, we see Louie struggle with some self esteem issues. Dewey is a natural born athlete, and Louie clearly is not.
I also feel like Louie considers himself pretty inadequate when compared to Dewey. There’s that low self-esteem again, probably along with some deep-seated envy. This isn’t near the problem with Huey as it is with Dewey; Huey, for one, is far less likely to be an insufferable show-off, and Louie genuinely has no interest in becoming a neurotic bookworm. Huey and Louie just don’t care about the same things.
Also, I firmly believe that there’s a physical dynamic to Louie’s ‘lovable laziness’ (see my ‘Louie has a congenital heart condition’ headcanon here) that probably plays into his complicated relationship with Dewey. Dewey is basically everything that Louie isn’t - athletic, brave, confident, brash - and so naturally Louie admires him, envies him, and might even be a little intimidated by him.
Which means that Dewey’s hot-headed insults are that much more hurtful.
We know that Louie is often the instigator, and oblivious, naive Dewey is usually the fall-guy (doing all of Louie’s laundry, etc). Dewey’s not an idiot by any means, but because he lives in solely in the moment, he’s easily distractible, and frankly, Louie can scheme circles around him.
But once the jig is up, Dewey isn’t the type to take this kind of manipulation sitting down. We know from season one that Dewey is fully capable of holding a grudge. We also know that he can be hateful when he’s angry. A slighted Dewey is all righteous indignation and reckless fury, and probably, he’ll say some things he doesn’t really mean.
Louie, for all his insufferable ‘i don’t care’ attitude, actually cares a lot. He is the most sensitive and sentimental of all the boys, and I just can’t see him as the type to stand there and hurl insults at his brother. He’s more likely to internalize his emotions, and he’s more likely to take what Dewey says to heart.
Dewey’s anger burns pretty hot. When he’s is offended, Dewey makes sure that everyone knows it. Louie’s a little more subtle. Staying mad takes effort, and Louie isn’t the type to waste energy on anything. Besides, we’ve already established that Louie is more likely to be hurt than angry. This translates as withdrawal, resentment, and, sometimes, sneering little digs that often fly straight over Dewey’s head.
For all of their differences, Louie and Dewey share one glaring similarity - they are both stunningly self-centered.
Apologies, when they come, are often days or even weeks in the making. In fact, it’s more likely that enough time passes that both boys end up forgetting why they were angry with each other to begin with, rather stooping so low as to concede defeat and offer to make up.
I don’t mean to villainize either of the boys, and I don’t mean to suggest that things are all bad, all the time (if anybody is interested, I can do a post on the brighter side of their dynamic later). In any spat, it’s rare for either party to be completely blameless. Dewey and Louie both have their flaws, but more importantly, they are just kids. Kids tend to mature out of stuff like this, and I fully expect things between Dewey and Louie to settle a bit as they grow up.
Of course these two love each other fiercely. Of course, when they work together, they are a perfect balance; Dewey brings the nerve and enthusiasm, and Louie lends his brother some focus and perspective.
It’s actually a lethal combination.