This isn't like a super serious end all be all thread about who's transgender or not in homestuck this is mainly just me assembling some ideas I've had floating around that might sound absurd as I work on a fic and as I've been getting through the vrisjune forcefem john vriskafication arc with a friend on its first time readthrough of homestuck.
Something my friend picked up on pretty much instantly and called "vriskafication" was that vriska gave june what was essentially a recolored version of her own outfit, and I read the author's note to it where hussie also calls it vriskafication because that is literally the exact thing that is happening is she's making june "the new vriska" both because of her new blossoming relationship and because she is plotting out a suicide mission in a kind of ill advised attempt to karmically clear out everything she feels bad about doing in her life, topped off by passing down her dice to june.
But a big thing with all her hero talk and making june into one is that for vriska, being a "hero" is an integral characteristic pillar of vriska's own relationship with being a girl. She feels in a way she probably wouldn't even think to articulate that part of what connects her to being a girl more than anything is being a hero, so naturally when she's trying to leave her mark on what june becoming a hero will look like, it just so happens to "coincidentally" look a lot like feminizing/vriskafying her.
In a related way: "hero" is just about the furthest thing from being a girl in dave's head. Her arc is about how she really really REALLY does not want to be anything like what Bro raised her to be - straight, heroic, a man - dave actually kind of really deeply hates all this, so dave's girl gender does not include "hero". For reasons I won't fully explain because I feel this is going to be a long enough post as it is, dave's gender includes "mom". Basics of this come down to her wanting to be pretty much the opposite of how bro raised her and sure you could take that in a lot of directions but I further submit dave's entry item and sprite, an egg and a crow who incubated it (which a dave would later combine with) and how dave later in the comic seems to have a strong fixation on moms, in a way that is easy to kind of brush off as a gag about how dave keeps blundering into freudian slips and hitting on relatives, but also I think is a bit revealing of her own personal desires. I'm not trying to convince anyone here this one is just my personal take.
IMO a lot of transgender homestuck analysis is figuring out what concepts a character deeply tied in with gender and specifically their own gender identity and teasing those out in ways that let you figure out how they're transfem.
Jade's girl gender includes "dog" in case you were wondering and this is the one I am least interested in defending so instead I simply will direct your attention to jade's reasoning for why she wouldn't wear a fursuit that while partially colored by a kids' "I'm not weird like those other furries" attitude actually has a lot to do with how it would be silly because it wouldn't actually get her closer to being an animal (and boy it sure is interesting what happens to her by the end of act 5 huh)