Iíve been working on a novel for years now which features three POCs as secondary main characters (the main guy is Greek/Russian). One is a black Canadian and the other two are Yupik Inuit and Mesoamerican (uncertain tribe). Neither of those two have much in the way of their modern lives written (at least online), and Iím curious if anyone here knows how to find proper resources for the marginalized groups which are less well-known than others.
Iím working hard to avoid stereotypes, though one of the two (Mesoamerican) has problems with English (not in a humorous way, I hope), and the other (Yupik) speaks almost perfect English, some slang included.
Should I try to find Yupik slang to add into her vocabulary? Should I have both speak perfect English so as to not possibly confuse readers into thinking itís a stereotype?

I can describe more about the characters if necessary, though this is more of a general set of questions, I suppose!

Basically...
How does one write cultures that thereís not much literature on?