Why can't I use "asuvat" in place of "elävät"?
How do I know this sentence isn't talking about humans living in the stream? For all the talk about wizards and shamans, things got awfully normative there :)
Why not ne elävät yleensä purossa?
Why does it matter where I put Yleensä? All previous examples had it mid-sentence for the same meaning so why not here?
If I had to guess, because in this situation they are stressing the "usually", whereas in other cases you might want to emphasize the stream (e.g. they live in the stream, usually.) Depends on intended meaning/ emphasis
What's the difference between ne and he?
"he" is for humans, "ne" is for pretty much everything else. Normally you'd say one is for animate the other for inanimate but you wouldn't use "he" for a group of animals