For lines of dialogue, create a new paragraph every time a different character speaks.
With such heavy accents I have to read some lines twice to get what they mean. It seems a bit much with the dialect, IMO. Then again, I don't know what the canon characters sound like.
These first 3 chapters are mostly back story, exposition, world building, and characters saying 'hi' to each other. I never really got a sense of character for any of them. Arnbjörn is nice, and... hard working, I guess? I didn't notice any defining characteristics for him, such as a conflict or fear or passion that he has, other than a fondness for this Berk place and the dragons they train. If I could say one thing for him, he's probably passionate about dragonkind in general and he cares about their having a good working relationship with humans. Though if that's true, then it could come through a bit more clear and strongly for the reader, IMO. In a way, you have shown us that trait instead of telling us outright, which helps.
Not being a fan in this fandom, I don't know what all this information about the world and the dragon types are supposed to mean to me, or what worth they'd hold for me as a fan, so keep that in mind. Real fans might enjoy it all a lot more, I wouldn't know.
For me, it feels like the story has yet to begin. Except maybe at the end of chapter 3, when the nightmares begin.
Sorry this is so short, but I can't think of much else to say. Fans of Ht TYD
would probably give you more intensive feedback.