Meiling is sleeping on the job in Hisoutenkou and BAiJR, so her being lazy is at least somewhat cannon (the extent is debateable). it's also true that Marisa gets by Mei Ling often. However, Marisa is hyper competent. For the most part, Akyu warns that you shouldn't disturb Mei Ling or do anything to her gate, so Mei Ling thus presumably keeps the majority of the riff rafff out (tho Akyu also thinks Mei Ling is meditating when Mei Ling is probably just slacking on the job, so I guess we can't trust Akyu's judgement on that one too much).
Patchouli describes Mei Ling as useless, but Patchouli says that for Sakuya too, so that doesn't mean much.
Unlike fandom, there is never any canon time when Sakuya physically abuses Mei Ling. At most, she snaps at her once when Mei Ling makes an admittingly silly comment in Strange and Bright Nature Diety regarding fairies. Otherwise, Sakuya generally seems nice enough to Mei Ling on a professional level (even taking Mei Ling inside when she catches her sleeping outside because she's worried about Mei Ling getting heatstroke in Hisoutenko. On a side note, this is a clear case of Sakuya catching Mei Ling sleeping on the job and instead of stabbing Mei Ling, she takes Mei Ling inside because she's worried about her. That's pretty much the opposite of fanon. ...on another side note, Patchouli remarks that youkai don't get heatstroke. Sakuya can sometimes be ditzy like that)
Sakuya herself is actually rather easy going, even when obeying Remilia's orders (she even says she doesn't believe that catching Lily will bring Spring to the SDM, but she's doing it anyways on Remilia's orders simply because such things keep Remilia entertained). There really isn't anything to indicate she's a psychopathic serial killer (besides the names of her spell cards). She's supposed to be the perfect and elegant maid, but fandom ignores that a lot.
Sakuya being a pedophile probably wasn't (purposefully) taken out of the cannon at all and it's a rather gross character butchering. Canonically, however, it is true that she does like fairies a lot (and fairies are childish) as shown by her attempts to recruit Cirno, the army of fairies in the SDM that she presumably recruited herself since she's the one in charge of hiring as shown by her ad in BAiJR (and apparently can even pick out which ones DON'T belong at a mere glance in SaBND!) and how extremely nice she was to Sunny, Luna, and Milky (whereas everyone else didn't even notice them). And she's generally happy with keeping Remilia entertained (even doing a sleight of hand magic trick for Remilia without Remilia requesting it in CoLA), but it doesn't get anywhere near into Sakuya nosebleed pedophile territory. If anything, Sakuya's probably just very motherly.
Yuyuko is clearly obsufucating stupidity (IE, pretending to be stupid). The latter stage dialogues of Imperishable Night clearly shows she knows what she's doing. She's actually able to predict what's going to happen next and merely covers it in a bunch of food analogies at several points in the story. Heck, she knows she's gone the wrong way before even Yukari does on that same path. This is also pointed out in Scarlet Weather Rhapsody, where she at first looks like she's just goofing off but eventualy she tells someone (Tenshi, IIRC) that she KNOWS what's going on and that Tenshi's behind it, but is really just playing along while waiting for someone else to solve it (it's not her job, after all). The same goes for Ten Desires, where her profile again states she knows what's going on (and her dialogue shows she even knows who's behind it) but is letting the heroine do it because... well, that's what the heroine is going to do. No need for her to get so involved.
Yukari is actually similar to Yuyuko in that regard. Except possibly a bit more proactive and more manipulative (Yuyuko sits back and watches. Yukari manipulates others into doing things and then sits back and watches after that. Both play the fool the entire time but are really just pretending to be stupid. Tho both will get directly involved if they feel they have to, as shown by the games where... well, they get directly involved)
Both Yuyuko and Yukari seem perfectly capable of reading each other and seeing what the other REALLY means even while they're playing stupid with each other, on a side note (their dialogues with each other in the fighting games). One reason why they're such good friends, I imagine.
To be honest, I really can't think of many times that Yukari went out of her way to troll someone JUST for the lolz. Every single canon portrayal of her always has her on the way to doing something that's important for the sake of Gensokyo, instead of just going out and goofing off for the hell of it. However, she certainly does troll anyone with the misfortune of getting in her way while she's progressing towards whatever goal she's shooting for. Presumably, Yukari doesn't waste time trolling someone to pass the time cause she's too busy sleeping instead. Yukari only plays pranks on someone while she's passing by, instead of seeking out people to play pranks on in the first place (and even then, her pranks usually have a purpose, too. Such as attacking the three fairies to gauge their power). That said, she can be gentle and sage like at times too (she often lectures people on how Gensokyo works, as portrayed/stated in CoLA where she politely lectures Reimu on why Reimu shouldn't be futzing around with the barrier just to summon her, or her win quote to Sanae in Hisoutenko where she says she hopes Sanae is enjoying Gensokyo. Also, Akyu states she's more than happy to talk about things and herself. It's just questionable whether she's lying or not).
