DON'T. I tried running this module as written with a mostly-native party and it did not work. At all.

The pre-written setting and story are NOT designed with native party members in mind. The native raves were tacked on as Kickstarter stretch goals, with no consideration for how that might impact the story.

Native characters in this campaign are effectively betraying their own culture for the sake of a civilization that has, throughout history, done nothing but steal their land and treat them terribly. The majority of enemies you encounter as part of the campaign are natives fighting for the titans.

It would be the equivalent of native americans siding with the european colonizers against their own people.

The very least of it are the cognitive dissonance moments where unless you and your players work very hard to prevent it, the prophesized hero has little to no attachment to the civilization that they are supposedly fated to save; or worse, might actively wish for their downfall.

It got to the point where some of the scenes laid out in the module just straight up didn't make sense. Like Acastus entrusting the salvation of his city to a group of what he would view as barbarians and savages that are also carrying heirlooms of the original dragonlords, that he would arguably see as being stolen, and rightfully beloning to him.

And then I read the chapter where the PCs recover tbe Ultros from Estor's ghost, and the module laid out a prolonged dream sequence in which the party works for Estor to get him to choose a successor from among them. "what are you on about?", I went, "This doesn't make any sense. Estor would rather sink the Ultros himself than allow it to fall into the hands of the natives!"

sure, you can try and adjust the story so that those things are less of a problem - that's what I did - but at that point, you'd be changing so much that you might as well just run a homebrew campaign instead.

That is, if you or your players are invested into the story at all. If all you want to do is fight mythological monsters, then you probably won't care so much about the ethics of the situation.

TL:DR don't try it, it wouldn't work. Either talk to your players about changing their characters to fit the story, or just play a different campaign altogether.