If this were a japanese comic Mikkel would be spouting a big manga-sweatdrop in that one panel. And that radio phone has been buzzing for who even knows how long, better answer it fast Tuuri!
Sorry guys, Mikkel's sibling situation shall remain a slight mystery for a little while longer. I saw many theories were had in the comments about what exactly "technically" maybe not being the oldest sibling could mean, I can tell you that one of the theories is spot on. And I think you'll all enjoy which it is once we eventually meet Mikkel's family. ;3