I tend to avoid even looking at old Norse saga profiles due to the proliferation of weird names and marriages and kids and whatnot.
To the best of my understanding, the father's profile has conflated Eystein Glumra and Sveidi sea-king. To cut and paste from wikipedia's page on Eystein Glumra:
Orkneyinga Saga also named Eystein Glumra as the father of Rognvald Eysteinsson: "Heiti, Gorr’s son, was father of Sveiði the sea-king, [who was] the father of Halfdan the old, [who was] the father of Ivar the Uplanders’ earl, [who was] the father of Eystein the noisy, [who was] the father of earl Rognvald the mighty and wise in council".
I've never heard of Alfarin, so I wouldn't guess whose son he might be; all I can say is that the old norse spelling is Eysteinsson. Oysteinsson is a modernism (and an incorrect one at that, as we'd use Ø instead of O).