Indeed. The provisions on DBC compensation are reasonably clear. The provisions on refunds, however, seem to have been written on the assumptions that: a)pax take return flights; b)pax go to one destination without stopovers elsewhere and c) pax pay for their flights with money. All 3 assumptions do not apply in your case.
As to UK vs Sweden, KLM UK CRs used to be very helpful when KLM UK was still a separate company and staffed by ex-Air UK staff from their base in Stansted. Nowadays, I would not be so sure. I have formed an impression of KL Sweden as a reasonably helpful bunch of people from posts on the KL forum. Might be worth asking on the FD forum where the most helpful team as between those two might be.
In any event, good luck and let us know how you get on.