Scrooge x Marley x Isabel AU shenanigans. No, it doesn't have to make sense, it just needs to be fun. To me. Personally.

But what IS Marley?

Yes, it's another one of those things were you need to find out on AO3 (18+ only)

I literally will never get tired of drawing Marley twirling his mustache. It's obnoxious, and I love him for it.

I cannot imagine Scrooge using any pet names when referring to Marley AT ALL. Just simply calling him Jacob is probably all the familiarity he can handle.

Now, Marley: definitelly address Scrooge as "lad" and "boy". Not even in a condescending manner necessarily (Marley does respect Scrooge, or else he would have never employed him) but just to remind Scrooge that he has seniority and is in charge. And then we know that, canonically, Marley likes to call him 'Old Boy' and 'Uncle Scrooge'.

With Marley and Isabel things would be, if anything, even more complicated. I like the idea of Marley calling her 'Izzy' once they become more familiar with each other (something @theoldandnewfirm first came up with.) The way he uses it, it's somewhere between teasing and adoring. Isabel is annoyed by the nickname, acts indifferent about it, and eventually begins to like it. I can sort of also see him calling her "lass" and "girl" in (almost) the same way he does with Ebenezer?

Isabel (besides only ever calling him Marley, and Marley only, no honorifics no title no nothing) probably likes to call him 'old man' whenever he REALLY manages to piss her off. I can also sort of see her using cutesy pet names like 'dear' or 'darling' in a sarcastic manner with him. Like, she'll call both Scrooge and Marley 'darling' in the same sentence, but the way it comes across for each of them is wildly different.