Since you're so interested in the concubines part, a minor update from the court of Jorvik. While furthering my quest to snatch Middlesex from the west saxons, I noticed that they managed to marry their heir to a East Francian princess. Yes, a real Karling (fun fact: in the original CK2 start there's only a single Karling left). Guess what came out of that hole when I captured their castle: an eighteen year old Karling, plus the queen of Wessex.
This game really makes you wonder why people stopped being viking