I have an idea that Japik's shield grog is a Danish sailor/warrior that was stranded on Rügen close to Crintera after a shipwreck. He was basically forced to join the covenant. Ardea and Japik lived in their cove but had regular contact with the main covenant and the Dane often sailed along the coast with a small boat to get them supplies they needed. That's how they came to know each other and some time before his apprenticeship was finished he was given him as shield grog. By that time the grog had fallen in love and married one of the female covenfolk so it was decided she would join Japik as well. I'm not sure what kind of servant she would be yet.
After splitting up with Ardea Japik and his two followers went west to Lübeck and Oculus Septentrionalis where they may have stayed for a while or just a few nights whatever suits the pre-saga. My thought is that Japik and Prochorus could have met here and since he was just about to leave as well they went together. Here they might have taken the land route southwest or they could have hired themselves onto a ship bound for the North Sea and came to Frisia that way.
They passed Japik's home village where they found it's fate and learned that Waddenzee was most likely involved in it. After that I don't know really but somehow they met Bernhard and he asked them to meet up in Anvers.
Wits, would this be ok for you and you might add anything to the story from when they left Lübeck?