There has been a Norse settlement on Orkney for many years. In the 9th century, King Harald Finehair of Norway established the Earldom of Orkney. Many earls have since governed there under the authority of the reigning Norse king.
Your father was a powerful leader. You were still a boy when he died. His land and title was passed to the 3 sons of his first marriage. Now Brusi is the only surviving son. He is your half brother and on good terms with King Olaf of Norway.