Why don't I have a go at making some demos in a Norse style for the main menu or the battle scene? I could take some inspiration from the music you've already got in the game. And you'd be under no obligation to use them if they don't fit.
Generally I prefer to keep the rights to the music (so I can showcase it in my portfolio) but grant the developer full permission to use the tracks for anything related to the game (in-game, in trailers, in promo material etc). That keeps things pretty simple in my experience.
Happy to talk further. My email is hughholbech@gmail.com or @miraduel if you prefer Discord :)