My thoughts on how the other characters would react to WhiteRose have changed somewhat since I first slid my way into this fandom, and at this point the way I imagine the Bees' reactions specifically is
At first, back in the Beacon Era, when Ruby and Weiss aren't even close to getting together but there are Moments, Blake and Yang both tease them over it. Yang slightly more than Blake. Think the "hey lovebirds!" moment in Dust Queen, if you've seen that
Once Blake figures out that Weiss might have Genuine Feelings for Ruby, she... doesn't say anything. She does, however, occasionally give Weiss a Knowing Look that she refuses to elaborate on, which annoys Weiss to no end, especially once she guesses what those Knowing Looks are about. Once Blake figures out that those Genuine Feelings might be reciprocated, she backs off entirely, figuring that the best thing to do is to give Ruby and Weiss time to figure things out for themselves
Yang... depends. On both the timeline for how WhiteRose develops and the timeline for Yang catching on
If Yang suspects that Weiss has Genuine Feelings for Ruby - or vice-versa - during the Beacon Era, particularly Volumes 1 and 2, I don't think she'd be particularly happy about it, mostly because I doubt she'd trust Weiss that much this early on. Though I doubt she'd openly confront either of them about it, the clearest she'd get would be a vague warning for Ruby to be careful, or having a talk with Weiss sort of like the one in episode 3 of Ice Queendom (the one that almost comes off as a Shovel Talk). Going with this interpretation could also recontextualize Yang's encouragement of Jaune and Weiss a little - "hey Weiss, you wanna date a team leader? because there's one right across the hall who's conveniently unattached and very interested in you and isn't my little sister"
If Yang figuring out that there are Genuine Feelings between Ruby and Weiss happens later, I think she'd be more supportive. Also, compared to Blake, more proactive in helping Ruby and Weiss work things out. Probably talk to both of them about it, individually, help them figure out their own feelings, and encourage them to talk to each other about those feelings. Or at least, Yang tries to do all that - how successful she is, is another matter, especially since I don't think she'd start either of those conversations by openly voicing her suspicions
Personally, I can see Yang starting to have Suspicions sometime after the Reunion at Haven, but not going far beyond "huh, I wonder if there's something going on between them", especially since so much else is going on that Yang doesn't really have time to wonder if her sister might be in love with the Ice Queen. But I'm also expecting some sort of Ruby/Weiss storyline in Volume 10 (I've made comparisons to the Blake/Yang storyline in Volume 6 before), and depending on how much of that storyline Yang is there to witness, that might be the point where she figures it out... and before she does anything else, she talks to Blake about it, at which point Blake reveals that she's already known about Weiss's feelings for a while, but not about Ruby's, and she didn't think it was her place to say anything. And at that point, they'd discuss what - if anything - to do with this information, with Blake favoring the "let them figure it out themselves" approach while Yang advocates for the more proactive approach, but they eventually settle on some sort of middle path
Meanwhile, Nora has known since late Volume 5 and has told Ren and Jaune, but neither of them believed her... except now Ren has his evolved Semblance and can confirm that Nora was right and that the WhiteRose Feelings are mutual
Also, Emerald at some point reveals that Team Evil has a betting pool about how each of the heroes' romance arcs shakes out and that if Cinder hadn't killed Watts, all the other bad guys would owe him money right now, Salem included
