Harald Køhler had two children when he was called out from his home in Denmark to fight in England. Jocelyn, eight, was the older of the two, and Margrethe, one, just shy of her second birthday. He didn't want to move his young children over to Britain, but arranged that if anything were to happen to his wife Linnéa, they were to be sent to a Viking controlled castle where they could be cared for. Jocelyn doted on her younger sibling and spent plenty of time around her. When Linnéa, twelve months after his departure, fell ill with a mysterious illness and passed on, the two were indeed sent to a castle as Harald had requested.
Harald visited his children, sometimes; concerned somewhat in case there was a raid. He got a promotion to General, and Jocelyn was very proud of her father. After about three months of frequent visits, hugs and bloodthirsty tales or battle, Harald didn't return for the Sunday visit. Margrethe and Jocelyn sat by the entrance and waited. When he didn't come, Jocelyn tried to put a smile on her face, if only for the younger child, now three, beside her. "He'll come to-morrow,Margrethe," she said. "He'll come to-morrow." But tomorrow passed with no sign of Harald, and with no news she had to keep telling her sister the same old lie, Margrethe growing more and more upset. Eventually, Jocelyn didn't know who she was trying to convince — her sister or herself.
Later, after about three weeks, Jocelyn got the news she'd been expecting; her father had been killed by British soldiers. Although she had long since expected such news, it didn't stop her being very much emotionally affected. Indeed, Jocelyn found herself to be very much devastated and almost angry, having always been closer to her father. The castle was empty walls — it was no Denmark, and it certainly wasn't home, with neither parent there. Even more than before, Jocelyn began to appreciate the company of her younger sister and the two grew exceptionally close, even for siblings. Jocelyn always got the sense that she was alone with her sister — it was them against the world. None of the lords actually cared and Jocelyn knew that, it was previously out of intimidation for Harald and now out of respect for him — it was never really about the two of them.
Jocelyn got closer and closer to Hogwarts age, but due to her closeness with her sister combined with the safety concerns of the Lord, she was schooled by the Lady of the castle, Lady Emilia, because it was deemed the Lady's best use of her time. Emilia wasn't the best teacher, and was never really a likable person, with little patience and less magical skill than the men, but they preferred to defend the castle. Jocelyn, tiring of the drab magical teachings, when she wasn't looking after her sister, found herself in archery ranges and training with the young males of the residing families in secret. It was during these sessions that Jocelyn made the decision that her slightly lesser magical skill didn't matter — she emulated her father instead, following in his footsteps as a warrioress.
Margrethe was a quiet child in general, and found joy in watching her sister from a safe distance. Although she was slightly disgruntled that Jocelyn wouldn't allow her closer or allow her to join in, she trusted her older sister completely and did as she was told. Although she would never admit it, Margrethe appreciated the magical aspects of the castle life much more than the clashing of swords. Margrethe had a much better relationship with Lady Emilia than her older sibling, and found joy in watching her often. Emilia could do enough magic to amuse the child — and although she very much disliked Jocelyn as much as Jocelyn disliked her, her like for Margrethe was enough for her to keep her training sessions quiet and amuse Margrethe while they were going on. Luckily, Margrethe was easily amused, and Emilia was an excellent liar, even to her husband's face, the Slytherin blood of her family shining through.
Jocelyn steadily became a great warrioress, but her attempts to rub the same attitude off on Margrethe were quickly lost. Margrethe had been influenced by Emilia by means of being able to stand up for herself, but was a much more likable person than the former. Shortly after Jocelyn turned of age, Margrethe had to bid Emilia goodbye. The two had been close, anyone with eyes could tell, but still nowhere near as close as Margrethe and Jocelyn. So, when Jocelyn decided that the two should leave the castle so they could live together in Hogsmeade, she sided with her sister rather than Lady Emilia and her husband. After protest from the latter side, Jocelyn and Margrethe gave their many thanks where thanks were due, and Jocelyn bought the two of them a small cottage in Hogsmeade village — purely because she wanted independence, and detected her sister's evident magical preference and wanted to get her a better education than Lady Emilia could have ever offered her sister. She did, however, have one request; that Margrethe was to spend nights with her at the cottage instead of Hogwarts. This was the product of years of being together, and neither one was prepared to be torn apart this quickly. They were together, independent and away from the fighting, and for them, that was all that matters. In Jocelyn's humble opinion, Margrethe, now in fourth year, is probably more skilled at witchcraft than she most likely ever was, but takes comfort in the fact that without magical assistance her sister will most likely never be able to swing a sword. Of course, Margrethe, as the caring, compromising young girl she is, tries to teach her sister a thing or two as she picks it up, in exchange for lessons in any form of weapon work. Both are picking it up slowly, but neither one will ever be as good as the other at their respective talents, and they've accepted that that's the way it has to be.