How was Fridlevus II related to Halfdan?
Fridlevus II Fridleif (Ynglinga saga) was a son of Fróði of the Skjöldung (Scylding) lineage. In that work he was the brother of Halfdan and the father of Áli the Strong.
Thorolf Kveldulfsson Thorolf Kveldulfsson (modern Icelandic: Þórólfur Kveld-Úlfsson) was the oldest son of Kveldulf Bjalfasson and brother of the Norwegian/Icelandic goði and skald Skalla-Grimr. His ancestor (great uncle) Hallbjorn was nicknamed "halftroll", possibly indicating Norwegian-Sami ancestry.