Keski-viikko is indeed Mid-week. The others look like borrowings near the proto-Germanic stage: cf German Montag, Sonntag. The Finnish words were borrowed from some Germanic stage at which the genitive endings were still present: *Monan-dag, *Sunnan-dag. But probably after the original ending (in *dagaz) had been lost.

Finnish has no F, nor initial clusters, so Perjan- could be from Freyja (or rather her counterpart in whatever Germanic language Old Finnish abutted).

The Finnish for king is kuningas if I recall correctly; this retains the *-az of Germanic (= Greek -os, Latin -us, still preserved in Icelandic -ur) so was presumably borrowed before the day names.