OOOH man, that's not something I've really thought about before. :O
I mean I can see why you'd think they might have some sort of relationship, all three are Scottish locos and they could've run on the same network at some point in their working lives, but I don't really have anything that deep for them LOL
I do, however, like to personally HC that Donald, back on his old railway, has always pretty much known everyone. It's just the type of engine he is, you know? Pretty much everywhere he goes he's making talk with whoever's there, being buddy-buddy, taking the piss, all that good stuff. He definitely had himself quite a few good mates that he'd shoot the breeze with whenever he wasn't taking a train. He's the charming, witty jokester, really outgoing and sociable, it makes sense to think that he knew a lot of engines (and they ofc knew him LOL).
So I would definitely say that, at least out of the two of them, Donald would be the most likely to have met Maisie at some point. And I do like the idea of her having met one or both of them at some point in her working life! She was a shunter/banker primarily, so maybe she banked one of their trains once or smth. That'd be a nice thought. uwu
But I guarantee that, like all the other mates they lost over the years, nowadays they'd definitely believe Maisie to be gone like the rest of them. Even though Maisie wasn't actually withdrawn until after the twins had left for Sodor [she was withdrawn sometime in the early 60s], they would have reason to believe she was withdrawn and, inevitably, scrapped. There were a ton of engines heading for the scrapheap, after all, they'd have reason to believe it unfortunately.
Either way, they definitely don't have any sort of relationship or knowledge of each other post-Donald and Douglas fleeing to Sodor lol.
TLDR; Though they did likely cross paths in their past, their relationship wouldn't have really extended beyond some friendly banter. And as it stands now, the twins might remember her as an old mate from the LMS, but that'd be about it LOL
(Likewise for Maisie; she'd probably remember them, but she likely thinks the same thing happened to them that nearly happened to her. ;;)
HOWEVER, as a fun tidbit, I was curious and found that the two sole IRL survivors of their classes [the 812s and 439s, respectively] are indeed aware of each other! :D Here they can be seen together -
So hey, even if D&D don't know Maisie anymore, at least they know her older sister?? Or... D&D's sister knows Maisie's sister...??? Ehh, I leave that up to y'alls interpretation! xD
(One final sidenote: I FORGOT HOW BIG THE 439s ARE LMAOO, especially when compared to the 812s! I did not consider that Maisie would actually be almost bigger then D&D... that's a really amusing thought. xD)
Thank you for the ask! ^^
