Maman Brigitte is the only white voudon, and her origins are in Ireland. She's traditionally red or brown haired. It's also why she and Mad Sweeney get on so well.
As for Nancy, his long game, like all of the gods, is to have sacrifices made to him so he doesn't fade away. Less black people = less sacrifices. But he is/was the trickster god, so screwing with people is kind of his thing. I think that's one of the things that makes his character interesting, there's something to be said about the usual, everyday, life-screwing-with-you stuff you could attribute to him and then there's the realization that his people won't be able to sacrifice to him because they'll be enslaved.
Anansi was accusing the Egyptians of creating a self-perpetuating trade, which would therefore reduce the number of potential worshippers of Anansi. Fewer black folks = fewer sacrifices. Anansi and Wednesday are still there because Cairo is pretty centrally located in the US. It's not in the middle, but it's not quite north, south, east or west. I'm not sure why Bilquis is still there yet, as she seems to be playing both sides. Could be she's found a fertile ground to start picking up worshippers for a while that's off the new gods' radar (as she'd previously been dependent on Technology, i.e. Tinder).
Argus recharged the coin, but Maman Brigitte's drink reversed some of death's effects. Combine that with ... ahem ... "being imbued with the essence of a god" (as the Greeks liked to say) and the clock got turned back a bit.
She wasn't healed, the coin was recharged, which allowed here to function. The she still had the autopsy scars.
The whole William James storyline is deeply bothersome. Actually, just about this entire season's ruminations on race have been deeply bothersome. You have these three African gods talking about their place in the scheme but no white people/gods around. You have lynching victim cursing future generations of his own people. Yes, it's no simple equation and self-loathing does exist, but this is a gross oversimplification. So what the point is? Who the ^&*% knows. Anyway, off the soapbox on that. The three gods laughed because Shadow is still so naive.