Yep, as others said, you can take it in the direction that you want. I have started with the Sulani pre-mades though I've just played them a little bit. Duane is a foster kid in my game. The Kealohas took him in as a way of tribal fostering but he isn't biologically related to them. Actually, Makoa Kealoha is descended from Japanese workers who assimilated into the culture, like what was common in Hawaii. He married Lilliana and became part of the tribe but biologically, he has no relationship to Duane.
Social services in Sulani are a bit different because the tribe has its own way of managing things. The Kealohas took Duane in but he is only living there until he grows up which happens as a teen in their culture. So, he works his own job, fishes and tries to fend more for himself. He's still a teen right now. I have no issue with him eventually marrying Nani if it works out that way, but he's not deeply connected to the family. They're just sheltering him in my game until he can be fully independent. His goal is to be independent as soon as possible.
That's how I'm interpreting him. I've also let the Sulani pre-mades develop other customs that aren't totally like the other worlds. You have to be allowed to own property there with a preference for the tribe. Marrying is a way of joining the tribe but it is kind of fluid. Households are not all "nuclear families". Someone is shipwrecked there and has to slowly discover the island.
Also, the royal household is all women and is matrilineal. They don't marry, they live as female heirs - kind of isolated. I haven't fully explored the pack but Sulani is a different culture in my game.