Is Eragon the son of Morzan?
Eragon is Brom's son. Eragon and Murtagh are brothers through their mother Selena. Morzan is Murtagh's father, but Brom is Eragons so that makes Murtagh Eragon's half brother. It was revealed in the third book Brisingr that Eragon's real father is Brom, not Morzan as it was told in the second book Eldest.