Googled: a lot of stuff related to linguistics, particularly conlangs, but at this point I'm not even sure how to narrow down what I need to research
So I'm pretty embarrassed at the non-specificity of this post, but I'm a bit lost with my world building at the moment.
I'm writing a fantasy story set in an AU of our own world. The MC is a offbeat psychopomp who, in the course of guiding her daily flock, makes a pit stop on a deserted island at the edge of reality. Every so often, for one reason or another, a bunch of the souls get left behind and thus don't wind up dying. Each time, she hurries on her way, figuring the worst they can do—living or dead—is shake some chains and file a complaint. By the time she returns to collect them, centuries have passed, and a society has sprung up in her absence.
The "pioneers" would be people of different cultural/linguistic backgrounds, so the structure of the society (as I currently have it) is very divisive. I figure that alliances would be fairly arbitrary at the beginning, then—as more people were left behind—they would split into groups based on their ability to understand one another. Within the groups based on shared language, there would be further divisions due to religion, ethnic difference, etc. Eventually, there would be social divisions between descendants of the "original" population and "new arrivals," who would be treated with superstition.
The story as stated is fairly lighthearted, but I still want things to make sense by some form of internal logic. So my questions:
1. What kind of evolution would take place over time? I assume that languages would acquire outside characteristics over time; after a couple hundred years they wouldn't resemble the original form at all (One of the bases I had for barriers between original descendants and new arrivals).
2. What mediums of communication would emerge for different lingual groups living in close proximity to one another? I figure that Creole languages would evolve between groups that interacted with one another often, and that these would rely a lot on regional context/gestures/expressions.
3. Is a "common language" at all plausible, and if so, what would it be? I assume that whatever group came out on top most often would force their language on those beneath them. But there wouldn't be a universally recognized central power as there would in most societies here, so I'm not sure.
4. How would the isolation of the setting affect all this? Would recognizable variants of Earth cultures be plausible? I'm considering that forces like colonialism and global migration would not be in play, and how this would effect social structures/gender roles etc., but I'm stuck between wanting to research a lot and get nothing wrong/considering that in such a scenario nothing would even resemble how it is IRL.
I'm not afraid of research, and I'll happily read anything you guys can recommend me. I'm just not sure where to start or what specific topics I should begin by looking into. I'm also happy to be corrected on any of my assumptions, even if it forces me to make changes to the story concept—I'd rather do it now, in the outlining stage, than a hundred pages in.
Thanks to everyone who took the time to read this post. This community has been so helpful to me on previous projects and I really appreciate it.