Theories abound concerning Mia’s age, but it could be merely an accounting error. Despite the fact that Mia is a decade or so older than Ensi, they could have grandsons of an age, if only just. But Torbjörn’s age is given as 38 in Y90, so he was born in 52. As Mia is at least seven-ish years old in Y0, this is quite the feat in the circumstances.
I think the theories presented include at least having someone purposefully removed from the family tree (because of? A scandal? A falling out?) or that Torolf is actually Mia’s son and Torbjörn is Torolf’s. Might be another one where the fans read tons on something that was actually simple oversight by the author
I don’t think Mia adopted, or at least not from outside of the family, because Emil as well as the terrible trio have strong family resemblance.
As for Kaino, her offspring wouldn’t necessarily be on the family tree. Minna has actually confirmed that she didn’t mean it to be 100% comprehensive, so the generations before our team may have offspring not listed. Possibilities everywhere!