I don't really have a source on this statement anymore but it was said that the two Cherubs kind of represented the audience, with Calliope representing the more over-the-top fanatics and Caliborn representing the haters. The latter strikes me as, even in the incredibly mean-spirited Act 6, extremely mean-spirited on Hussie's part for reasons that I'll get into.
At least there is some self-parody involved here with Cherub reproduction being a weird joke at what nonsense Troll reproduction and relationships were. Them forming an AURYN sign also feels like a gag about how much the Huss uses distinct symbols for characters, etc.
Calliope is overwhelmingly positive and cheerful, to the point where her messages are described as "cheers."
She uses a UU username to fit the pattern established by the ACGT abbreviations and the "DNA" theme - uracil is a base that replaces thymine in RNA, which maintains the theme while still allowing room for a character to be a super-special OC of the "Sailor Earth" type - one that tries to trick out the pattern showing that they understand the pattern just enough to not understand it in the greater significance.
She's also shown dressing up as Calmasis - signifying an enjoyment of characters so minor even the author probably forgot them, something not necessarily uncommon to a superfan - as a troll. By this point, troll cosplay was not unheard-of and was already infamous for the horrible messes it caused and the fandom seemed to be deemed a bit of a problem at some cons. I remember this era of following Homestuck stuff on Tumblr.
Her fantroll is given a dirt-obvious name: "Callie Ohpeee." I'm pretty sure this is meant to be mocking. Or, er, "gentle ribbing." But Hussie isn't good at gentle ribbing.
Calliope speaks with a lot of British-isms. I assume a lot of fan characters used weird word choices to force a quirk but I don't remember. For sure, a lot of fan typing quirks were overbearing; of course the canon ones already were so they were kind of in good company.
Caliborn is a gross awful little misogynistic shithead. Being that he's supposedly based on Homestuck's haters, giving him this personality suggests that this is what Hussie thinks of people who hate Homestuck. Considering how badly Homestuck treats a lot of its female characters, there's a special something gross about this.
Caliborn is implied to have a learning disability. Being that he's supposedly based on Homestuck's haters, giving him this trait suggests that this is what Hussie thinks of people who hate Homestuck. "Sorry you don't like the webcomic, you must be a r****d!" Nice. Real nice. Real fuckin' nice.
Caliborn only talks to Dirk because he's the only one he considers manly enough for that sort of thing. I assume he's said some slurs about Jake and his Lara Croft belt.
Caliborn is way too into overly-complicated shit - it sounds weird considering Homestuck's reputation for being completely bugfuck nonsense, but Caliborn also loves worldbuilding, which Hussie seemingly does not.
As the resident hater, Caliborn is constantly bitter and vitriolic and hates things. He "jeers" others and uses a "tumut" emote a lot in an attempt to represent him giving the other person the double deuce.
At one point, he openly whines about how long things take in the characters' lives... and ergo in the comic itself. This mirrors criticism of the comic being absurdly long-winded.
Despite his seeming affinity for worldbuilding, he constantly gets certain things wrong (like what the Leprechauns are actually called). Because he doesn't actually read. Joke here about RPG players.
Caliborn, at first, cannot draw. Not that he's any good later, but his early attempts are just straight lines. Eventually he reaches a point of drawing a circle! Made entirely out of straight lines. I am not sure if this is tied up in the learning disability part, or if it's just supposed to suggest he refuses to change course and just tries the one thing he knows until it bears fruit. Probably it also is a jab at the people who don't like Homestuck, on some level.
While there's an explanation for both Calliope's shipping and Caliborn's ideas of what constitutes pornography due to Cherub Reproduction Being Fucked Up, I also kinda wonder if he's trying to say something else here, either implying an inexperience for the haters (basically a sideways way of calling them virgins), or if it somehow relates ot the what is mostly much-more-recent phenomenon of people making the same joke where they will describe hand-holding as prime filth or similar. (It's probably not. But it's funny how this ends up.)
Caliborn ultimately becomes the major villain of the piece. Making someone supposedly based on your critics into your final boss is... a choice, alright! Same goes for the fact that Lord English went from being "giant demon who cleans up dead universes" implying a certain kind of duty to a petulant douche looking for his dead sister to kill her again probably because of misogyny.
Somehow I forgot to mention this when I first put this together: Caliborn loves games. Like, a lot. On one hand, I think the gag here is that Hussie is making fun of people for caring too much about the gaming abstractions like grist, alchemy systems, or the build menus after they'd long outlived their usefulness to the plot. On the other hand, his obsession in particular with competitive gaming means that he kills Calliope's dream self (indirectly), destroying her personality and making him predominate over her very early - so early that he hasn't finished developing, and he never will grow any more as a person. Mostly I like this because I have had very poor experiences in practically every competitive game, even at very low levels.
I had more things to say, probably, but I've focused very heavily on this one point the whole time, and that's probably really dumb. But it also makes Hussie seem like a huge pissbaby toward his critics. Maybe the pissbabiest a person has ever been toward critics if it's true.
With Hussie's general disposition toward his fans, I'm kind of surprised that Calliope ends up becoming such a major, important force for good.
As to the other one... Look, artists and critics frequently make enemies of each other. I wouldn't say "no artist likes their critics," but it's pretty common. Many critics kind of suck at their job, many artists are not good at that part of their job. I've seen versions of this that are significantly meaner; a great example being Michael Crichton in Next, using almost the name of a critic that gave him a bad review for a minor character who is on trial for raping a toddler and is pointed out as having a small penis. Hussie didn't call his critics tiny-dicked pedophiles. In fact, he didn't... really accuse any of them of any crime at all unless we want to pretend he is literally suggesting all the people who don't like his work are murderers, which would be a stupid thing to say. But it is enormously petulant from a man who would continue to be enormously petulant, and look, I know Homestuck's fanbase in the early 2010s was infamously insufferable, but I just think this is a poor way to deal with it.
It's sort of a pity that this hangs over Caliborn, because he is such an annoying, shitty person that at times he IS entertaining without being tedious in the way that Doc Scratch often is.