We answered your first question in another Q&A, so I'll copy/paste it here.
Lan, the Nicest Orc: Regarding the new arrivals, was research into their particular myths/culture hard? What were some of the tools you used for that research?
NANOFF: As usual, our research involves tons of googling and watching videos and movies and consulting with people from the respective countries.
Themba was by far the hardest character to design for the game. Sub-Saharan African mythological creatures aren't as extensively portrayed in Western media so we had to do a lot of research to do. We had another issue: the game already has an abundance of both heavyset characters and reptiles, and a lot of African mythological monsters tend to be giant aquatic mishmashes of reptiles and large mammals (which, you know, considering the kind of stuff you find in African rivers is not surprising). The grootslang was the most fitting creature for Themba's role as the hotel's accountant, considering it's a creature that guards precious gems, and one of the better known ones, we played up the elephant elements of the design. We also did research on Johannesburg since the city influences Themba's personality and backstory.
MINOANON: Zaggy Norse helped us a lot with this. Doing our own research is good and important, but nothing beats having a chat with someone who's actually knowledgeable with the culture itself.
NANOFF: Khenbish was also tricky because A) I swear to god there are no decent public domain/non commercial license pictures of Ulaan Baatar, and B) we couldn't find anyone from Mongolia to personally consult with. The best we got was getting a friend who went to school with a Mongolian classmate to ask him some questions, and we managed to get some information from him. We complemented our research watching two movies: the Eagle Huntress, and the Story of the Weeping Camel. It was an interesting case for us because a lot of Mongolians were upset with Eagle Huntress (produced and narrated by Daisy Ridley) overstating the amount of opposition the protagonist was up against for trying to do a male dominated activity — there's a lot of close ups of old men looking angry while everyone seems chill in the crowd shots, you can tell that it's trying to force a narrative. It was a good reminder to never be satisfied with a single source when doing research on a foreign culture.
MINOANON: Because we couldn't rely on someone to consult with, we had to be more creative in our research. Beyond the sources nanoff mentioned, in the end I'd say one of the biggest inspirations for Khenbish came from us reading Mongolian poetry and studying what structures they use. We tried to incorporate some of it in the writing. I don't expect many people to take note of it but I'm proud of that aspect of his content.
We covered Khenbish and Themba, who come from Mongolia and South Africa respectively. But there's also Storm and P, who both come from Brazil — more specifically, they come from a part of it with which I am very acquainted and from a very specific economic and social situation. For them I was overwhelmingly pulling from the folklore and mythology I was personally familiar with. That's probably the main thing about it — while we tried to explore different cultures with most of our characters, in the Hinterlands I was fully diving into my own and going as far as I could.
Because of this, the Hinterlands probably had the richest mix of sources. For the record, I should add I also read some Câmara Cascudo (a Brazilian folklorist) for ideas, and that really played a role in the story.
---
As for Hades and God of War...
Here's a fun story: while visiting a family friend as a teen, I saw his son playing a God of War game where he was killing minotaurs in extremely gruesome and graphic ways. I sometimes get freaked out by extreme video game gore+violence and that's one of the times it happened. I don't think Asterion would like it either.
He'd enjoy Hades' story, kinda. He'd like how Persephone and Zagreus are portrayed, he'd be into the main storyline of them reconnecting, but he'd disagree with how Hades comes across and generally have a hard time verbalizing his thoughts about the portrayal of the Olympians, Asterius and Theseus.
He'd be very annoyed with the in-game lyre not having a minigame associated to it, and he'd be into Orpheus' songs.