Well, the Basilissa's husband is a Swede, and it's a regular marriage, so the ERE will become Swedish. Question is, why isn't it the first son who will inherit? Bastard? Or is this an elective monarchy here?
First son was probably born before she came to the throne, second son was born and thus is the only kid with the 'born in the purple' trait. The oldest kid with born in the purple supercedes all of the other children, IIRC.