I like Leif & Forrest the most with Kasper Snow and given your heritage. Leif (Layf) is so poised but outdoorsy and handsome to me.
But I don’t think I would use Oskar with Leif. I prefer a consonant after Leif - eg Leif Magnus or Leif Joren.
Having said that, it is a balanced (both calm & spunky) name, Leif Oskar.
I like the idea of Forrest Svein. But also Forrest Viggo could work?
I’d opt for Marlo if you want to lean into the hip/artsy feel of Kasper but I think you should stick with one of the more weighty names of Leif and Forrest.